We have a jack knife sleep sofa and you can really feel the edges of the different sections when it's folded out. I usually grab the pads from the dinette and put it on top for extra padding. For a more long term solution, I'd go with a memory foam topper, but I only sleep there when I get kicked out of bed for too much snoring. I've thought about this solution as well, which offers a little more than your standard topper:
Sleep Master Memory Foam 4 Inch Tri-Fold Comfort Mat