There are a number of varieties out there and they differ wildly. Don't go for the bargains - in this case you will get what you pay for. The construction matters a lot - body heat retention, body impressions, etc. Do your research and a lot of it before making a decision. Read reviews on as many sites as you can to learn the difference, and to find out what people like/don't like about the mattresses. I just bought a new Serta traditional mattress but with a fairly thick eurotop on it and I love it. Kind of the best of both worlds. And it's lightweight and easy to move, to boot (I've read that the foam mattresses are very heavy and difficult to move). Good luck!