You might want to look into the air over coil mattress. We have one in our Villa sofa bed and I've been very pleased with it. Essentially, it uses the coil mattress base with an air mattress on top of it. Since the air mattress portion can be deflated for storage, it folds up into about the same space as the old, uncomfortable coil mattresses. While I'm not a fan of either air mattresses or the lousy coil mattresses, the combination in this mattress is remarkably comfortable.
David, Judy, Gracie (the dog) and Waldo (the parrot)
2013 HR Endeavor 43DFT, 2014 Ford Flex