I could never find a bed I liked until I purchased a memory foam mattress. I went ahead and got a pillow, too, for better neck support. Memory foam comes with one major downside in the summer, however: it retains heat. Technogel solved that problem with a gel layer that keeps your head cool at night.
I live in a hot apartment where air conditioning doesn't make a huge difference at night. I sleep with only a top sheet, and I had to purchase new sheets because even that was too hot. While more breathable cotton sheets made a difference, I happened across Technogel pillows recently. I decided to buy one and give it a try and it actually keeps me cool at night. At first it feels a little too cold, but once your heat transfers you reach a happy medium.
The major downside is that the pillows cost a lot. You can pay more than $250 for one of these babies locally.
If that's an issue, there are plenty of other ways to stay cool while you sleep.