What's prompting a new toddler mattress?
- The cot bed is converting
- We've been handed a used one
- Leaks and night-time accidents
- They're asking for a pillow and duvet
Firm, flat, waterproof and snug are the essentials
The mattress needs a firm, level surface and proper protection from moisture, with a snug fit all round. The Lullaby Trust's mattress guidance says the safest mattresses for babies are firm, flat and protected by a waterproof cover.3 It also says to check the fit and condition, including rips, tears and sagging. That's where I start for a toddler's mattress, however persuasive the photograph of an impossibly tidy nursery.
- Firm: choose a surface that stays supportive under your child. A soft top or deep quilting is the wrong direction, even if you find it inviting when you press your hand into it.
- Flat: the surface should be level, with no sagging. A dip in the middle is a reason to reject it, even when the cover looks spotless.
- Waterproof: the mattress needs a waterproof cover. A washable fabric protector over the top is useful, but washing that protector won't undo moisture that has reached the mattress inside.
- Snug: check the mattress against the bed's required dimensions. The Lullaby Trust's fit guidance is clear: there should be no gaps round the edge.
The Lullaby Trust also names the mattress standards BS 7177 and BS EN 16890 for cot mattresses, and includes a fire-resistant label among its second-hand checks. Check the fire label when you choose a mattress. A reassuring product name is a very easy thing to print; I care much more about the actual label and whether the mattress fits.
In October 2026 we emailed Jim Oram, a policy officer for home safety at the Royal Society for the Prevention of Accidents (RoSPA). We asked him which safety points come first for a toddler's mattress and the bed it goes in.
While your cot bed is a cot, check for the cot mattress standard on the label, and when it becomes a bed, ask the maker what the mattress should meet. Keep the bed's instruction sheet where you'll find it, so you can check again for another mattress or child. If standards aren't listed, ask in writing which ones the bed and mattress meet, so you can hold the retailer to that. Then look at the mattress surface.
For a toddler, my preference is a plain, firm top that you can keep clean. The cosy appearance of deep quilting gives you no reason to abandon the firm, flat surface. Keep softness out of the mattress decision, and leave advice about bedding to the NHS and the Lullaby Trust.
New is simpler; second-hand needs every check
I'd buy a new mattress for a child's bed where the budget allows, because its history is straightforward. Second-hand is an option only when you know its history and every Lullaby Trust condition is met. A family hand-me-down can be useful, but "it looks all right" is doing a remarkable amount of work if nobody remembers where it's been stored.
The Lullaby Trust's conditions for a second-hand mattress are specific:
- It has a well-fitting, fully waterproof cover.
- It has no rips or tears.
- It has no water damage.
- It is firm and flat, with no sagging.
- It fits with no gaps.
- It carries a fire-resistant label.
My additional buying rule is that you know the history. Inspect the mattress and cover before agreeing to take it, because a freshly washed sheet tells you very little about what's underneath. If you can't establish whether it was soaked or stored damp, choose another mattress. There's no saving in bringing home something you'll need to replace.
The size still matters when the mattress comes from someone you trust. A cot mattress doesn't become a cot-bed mattress because both belonged to the same child. I admire a determined attempt to avoid another purchase, but the dimensions have to match the bed.
A cot bed keeps its mattress when it converts; a different bed needs a size check
A cot bed converts to a small bed using the same correctly fitting mattress, while a move from a separate cot to a cot bed requires a different size. Check which change you're actually making before ordering. "Toddler" on the packaging is rather less useful than a tape measure, however sweet the packaging.
These are standard UK sizes. Check the dimensions specified for your particular cot or bed as well, because the mattress still needs to fit that frame properly.
| Bed type | Standard mattress size | What that means for your purchase |
|---|
| Cot | 60 by 120 centimetres | This is smaller than a cot-bed mattress and won't fit a cot bed properly. |
| Cot bed | 70 by 140 centimetres | The same mattress stays with the cot bed when it converts, provided its condition remains suitable. |
| Single bed | 90 by 190 centimetres | A first single bed needs its own correctly sized mattress. |
Once you're shopping for a first bed, access becomes part of the decision. A low bed, or a mattress close to floor level, makes the climb in and out shorter while your child learns. A bed guard is another first-bed consideration. Check the bed and mattress requirements for any guard before buying; the NHS and the Lullaby Trust are the places to go for advice about its use. The miniature-house bed can wait until you've checked the practical bits.
The second thing we asked Jim was what parents should check when moving a toddler from a cot to a bed.
Move when you notice one of his signs, whatever age is printed on the box or bedding bundle. The room check is easy to skip when you've relied on the cot to keep your child contained. Work through his list the week before the bed arrives, while you're still using the cot, so nothing is rushed on the first night. Your child still needs the same firm, flat mattress surface in their new bed.
The firm-surface principle also appears in US infant guidance. The American Academy of Pediatrics' 2016 policy recommends a firm sleep surface and avoidance of soft bedding: the same firm, clear sleep-surface principle for babies.2 Safe to Sleep, from the US National Institute of Child Health and Human Development, likewise advises a firm mattress that fits snugly with no gaps. Both are guidance for infants, not toddler-specific recommendations.1
A move into a bed doesn't settle the question of pillows and duvets. Follow the NHS and the Lullaby Trust for the timing of those for an older toddler. I wouldn't use a matching bedding bundle as the reason to introduce either.
Use waterproof protection and make cleaning straightforward
Choose a wipeable waterproof cover with a washable protector over it, because accidents are much easier to deal with when moisture hasn't reached the mattress. This is one place I'm firmly in favour of a protector. A spare washable one is a useful purchase when the first is still in the wash.
Foam and pocket springs can both suit a toddler's weight if the finished surface is firm and flat. You don't need to select the most elaborate construction. Look at the top as well as the core: a firm mattress with a soft, deeply quilted top still has that soft layer against your child. My preference is the simpler, wipeable option.
After an accident, wipe the waterproof cover and let it dry and air before remaking the bed. Wash bedding weekly, and sooner when it's soiled. Cleaning is also a useful opportunity to check the cover for damage. Nobody puts that task on the nursery mood board, but it's how you'll spot a tear before the next accident.
Replace a mattress that has been soaked through and hasn't dried out. The Lullaby Trust requires a second-hand mattress to have no water damage, and I apply the same condition check to one you're continuing to use. A dry sheet over the top doesn't tell you whether the inside is dry.
If the mattress arrives rolled, follow the maker's full expansion time before use. It needs to reach its intended shape so you can check the surface and fit properly. Unpack it ahead of the bed change; ordering around the delivery date alone leaves you with less time to get it ready.
When you're choosing for the next stage, our children's mattresses are a useful place to compare options for a larger bed. Keep the frame's required dimensions beside you while you compare, so you buy the right size.
For everything about how a baby or toddler sleeps, follow the NHS and the Lullaby Trust's safer sleep advice. Their guidance on sleeping position, room-sharing, bedding and what to keep out of the cot is the advice to follow, and it is kept up to date.
We also asked Jim when a toddler's poor sleep is worth raising with a health visitor or the GP. A new mattress sometimes gets bought in the hope that it will fix the nights.
If bad nights are the reason you're shopping, call the health visitor before you buy anything. Start the diary he describes before the appointment, because the practitioner needs to see the pattern across the nights you're having. I wouldn't expect a mattress to fix the nights, so buy it for the move itself. Keep his last sentence somewhere you can find it at two in the morning.
Leave soft tops, gaps and damaged mattresses out of the basket
Reject a mattress that fails the surface, fit or condition checks, however convenient the purchase would be. I know "we've already got one" is appealing; it still needs to be the right one. A pretty cover is equally unhelpful if you find a dip underneath.
- A soft or deeply quilted mattress: looking cosier doesn't make it suitable. Keep to the firm, flat surface described in the Lullaby Trust's mattress guidance.
- A mattress that leaves a gap: the Lullaby Trust's snug-fit condition still needs to be met.
- A second-hand mattress without full waterproof protection, or with sagging, rips or water damage: these fail the Lullaby Trust's conditions.
- The old cot mattress in a cot bed: the standard sizes are different, so it won't fit properly.
- A mattress without a waterproof cover during the accident years: choose waterproof protection from the start so you can wipe the surface clean.
