Over the last couple of years we have upgraded all of our mattresses to either latex or latex hybrid mattresses and are very happy with them. Note latex is nothing like memory foam, which I can't stand, Latex is springy like a good innerspring mattress just with much more even support, out of the ones we have bought the best bang for the buck came from a small mattress company in California by the name of Flexus Comfort, they have a fairly basic web site, but make a good product, ours arrived in a box marked Nest mattress with a label on it that said that it was really a Flexus Comfort mattress and that they had previously been a Nest mattress manufacturer and were being evironmentally sound and using up the Nest boxes. So I went to the Nest web site which as fancy and talked about planting a tree with the profit from every order, etc. and saw that they offered a nearly identical mattress to the one I had bought that was priced nearly twice as high.
p.s. note they will do custom RV mattress sizes, you just need to get a custom quote