So I've built myself two mattresses using just a 12cm thick slab of foam. My girlfriend and I both consider my "mattress" to be the most comfortable we've ever slept on, and guests that have tried it found it very comfortable. Initially I planned to add other layers to it, like latex, gel, springs or whatnot, but I really can't find any reason to.

It's a fine temperature in the summer and nicely insulating in the winter, and it was fairly inexpensive too ($140 for two 100x200x12cm slabs of high quality foam.)

Has anyone else tried this simple approach to DIY mattress building? Any thoughts on why (or why not) to just use plain foam?

[edit] The reason why I ask is because maybe there are hidden factors I haven't considered. Maybe there's a risk of back pain, or less deep sleep, or something I haven't considered. Perhaps the most comfortable mattress isn't always the best for you. I figured if there's anywhere I'd find a subject matter expert, it'd be here :)