For what it's worth, my wife and I went to Macy's, years ago, and tried every damn mattress in the store. We settled on a Macy's brand firm mattress. It's got some memory foam on top, but it's not a pillow top. You didn't say whether you got a firm or soft mattress, but that may be part of your problem. If you sink down, then you've got more of your surface area against the mattress, and that means more thermal problems.