Go on eBay and search memory foam mattress toppers. They come in many thicknesses and densities. We put a 4 inch medium on the MBR mattress and it feels like a dream.
For a fold out or dinette, I'd go with a 2 inch, which rolls up tightly for storage. You may also be able to squeeze it under your MBR bed.
For the sofa, you MAY be able to leave it on when folded up as the creases pop out when opened.
Craig and Susan
Morgan Hill, CA 2007 Newmar Kountry Star 3910 towing a 1998 Ford Explorer. RVing since gas was 58 cents a gallon. Amateur Radio Operator (W6ADV) since 1962.