You can try your local Jayco dealer to see how much they run or have an upholstery shop make one. Another option is to pull the cover off the mattress, get the dimensions off the foam and cut a replacement from a better piece of foam. Kohls carries some memory foam if you want to upgrade the mattress and some fabric or upholstery stores have generic foam you can cut to fit. Wash the mattress cover and throw it back on some new foam and you should be good.
2013 26BH ghetto model w/ 4 plain rims and some rust
2001 Silverado 2500HD 6.0 gasser
I have a fever...and the only cure is more camping!