I have replaced my mattress and my guests always comment on how well they slept. I ordered it online. It has an air chamber on top that of course adjusts to individual comfort levels. I googled to locate vendors. Try this one, they have an over the top air mattress.

Here is a link that might be useful: seating system

Wow that's awesome sewlutions! I wish we had a sofa sleep to get one of these for. I also like the idea of the air bed that turns any sofa into a sleeper. We already have an air mattress camping bed that is very comfortable, but their system would save space in the room since our three guests rooms are being used by our son and grandson. Two as bedrooms and the third as their living room. The later serves as our guest room, but already has a sofa. Thanks so much for sharing that link.

Whoa! They have an awful return policy though.

Just following up on this thread to see if @justgotabme got one of the mattresses. I'm considering a memory foam mattress for the sofa bed in our 2nd home. Was wondering if the air mattress was better.

Sorry Gooster, I started to reply to this yesterday, but our new bed arrived.
No we did not get one of the mattresses. I never took time to see if anyone sold them locally. We did however get a new bed for us and am loving it. I'm sick with acute viral bronchitis and its adjustability was wonderful last night and throughout the day when I napped. I'm in it right now. I could almost live in this bed when sick like this.

How thick is the original mattress? I'm shopping for a replacement as well, and I came over this one at a reasonable price which is available in both 4" 5" and it has pretty ok reviews.

Please let us know how the mattress you'll buy behaves :)

Here is a link that might be useful: gold quality sleeper sofa mattress