Guided by the excellent sales assistant, we did extensive tests in the shop to find the right mattress to replace our very old Hypnos mattresses, but what sealed the deal for us was Dreams' 40 night exchange deal. I'm by nature risk averse, it's a major purchase, these mattresses are not cheap by any standards, so that security meant there was no gamble.
Not a problem really but we were buying 2 x singles and all we could test was a double. That said, the mattresses are pretty firm and there's no "edge roll-off" effect so you can use the whole width. (We have them on sprung slatted bases.)
Also I would suggest do not overlook the value of testing with the right pillow hardness and height - it makes a huge difference.
So far, sleep has improved significantly.
They are very deep with the built in topper so the top of the bed is very high for getting in and out which may be an issue for some (not us). Plus you need to buy deeper fitted sheets.
Longer term I'm a bit worried about them not being turnable but if there should be an issue with that, hopefully Dreams' 10 year guarantee should cover that.