Hi I did a lot of research on this thought I ended up with a Latex mattress instead (feels more like a regular mattress rather than sort of sucking you into the memory foam -- but it's very springy, so I feel every little movement my husband makes, which I don't like), but in terms of memory foam, the Sealy brand is just as good as the Tempurpedic and much cheaper. The heat issues were primarily around the first releases of the mattresses -- now they have air vents and the newer ones don't make people as hot.
Also, you should definitely bring a book and spend 15 minutes laying on the mattress before you buy it. It softens with body heat, so if you just lay on it for 1 minute in the store, you might find it's too soft for you if you're on it all night (the memory foam mattresses also now come in different softnesses).