I've been looking into DIY concrete countertops and sinks for one reason or another and somehow that got me to a site where a person describes making their own mattress. A mattress is just one of those things I thought you needed a factory for. I'm starting to think there are a lot of things I could make myself and actually don't need a factory for.
Anyway, here's the link! It sounds like a very comfortable mattress.
Here's a diagram of a foam mattress should anybody want to do some research!