When I got my truck it had a nylon covered slab of foam for a mattress. It was used. I asked them to put a new one in and it is a two sided mattress with springs. I love it.
A word about memory foam, it freezes. A friend of mine has one. After it sat for several days while visiting family for a few days in cold Colorado, he got a surprise. He returns to his cold truck, starts it and falls into his memory foam bed, thud. It was frozen solid.
Sounds like maybe he started with a water bed...?