D.P.
Personally, I would try the foam (egg crate type) topper. at least you could roll it up and store it in the corner of a closet. I hate air beds!
I don't think sofa beds or the sofas that have beds in them are ever very comfortable. Good luck!
(Cue Elaine from the Seinfeld episode: "This BAR in the middle of my BACK!" lol)