Bill, the mattress business (land or sea) is radically overpriced. If you can find a foam rubber manufacturer or supplier in your yellow pages--they'll be at least 1/2 cheaper than any mattress store for the same foam rubber goods.
There are also a number of "bedding" stores on the web that will sell foam rubber mattresses cheaper than most local stores. Don't think you can use a "topper" as a mattrress, the toppers are designed to crush down under your weight and just supply conformation, they are not firm enough to be used alone as matresses.
Somehow I grew up and lived on no more than 6" of mattress, the bedding stores today say I couldn't possibly have slept on less than a foot of padding. (Yeah right.)
A carpet "steam" cleaner, rented from a supermarket or hardware store for $25/half day, makes a great way to clean upholstery. And your car interior while you're at it. Just give it good time to dry out afterwards!