After owning a Silentnight Firm mattress for the last 5 years, I was surprised that the new Medium Firm one was so much firmer. However, I put this down to the new one needing time to settle and that the new ottoman base was probably a bit more rigid than the rubbishy old divan.
The old mattress was a comfortable old friend. Supportive, warm, slightly snuggly. Even before the new one arrived I was feeling guilty for getting rid of the old one and slightly panicky that my wonderfully comfortable bed was going to be replaced by an interloper!
I needn't have worried. It only took a few nights' slumber for Medium Firm to live up to its name. It is indeed less firm than the old mattress, the topper panel thing provides more snuggliness than the old one. Even better, my lower back pain has significantly reduced (I sleep on my side and I don't think my hip was sinking low enough in the old mattress).
Due to mixing and matching brands for base (Therapur ottoman) and mattress, I do feel a bit "princess and the pea" due to the combined height of the bed. It's now at least 6" higher than the bedside tables. That said, the sides of the mattress don't "collapse" when I sit/lie on the edge, so it's not like I'm unceremoniously deposited on the floor from a great height if I try to sit or lie on the edge.
All in all, very happy with the combination I went for.