It's likely that a sofa sleeper will never be the best bed you ever slept in. But they don't have to be so uncomfortable.
Here's what I did:
First, you need a new mattress, best I think is 5" memory foam. Try to find one as close in size as possible, but you will need to trim one side and one end a couple of inches probably. Now for a lot of people this should fix the problem with the bars that everyone usually feels with sofa sleepers. But not for everyone. I have a buddy that goes with us that is 6'4" and 250 lbs, another that is not tall, just 300 lbs fat. when we go with one or the other with their wives they will sleep on the "pull out". The memory foam on it's own, while and improvement, isn't enough so here's what I used:
Medium Density Fiber Board2 pieces of this fiber board with 3 inches trimmed off one side will fit together perfectly under the memory foam mattress. No more bars to feel while sleeping. And as a convenience, after folding in the sleeper, place these boards one on top of the other on the fold out, place the cushions on top and you're good to go.
My ex-bro-in-law went with me one time and said he was dreading sleeping on the pull out but just figured he would "rough it" for a couple of days. On the way back he said he got a better nights sleep every night on my sleeper sofa that he gets in his bed at home. :C
