Worst purchase ever. Never buy a Sealy!

We had a great experience at the store. This mattress seemed like a good buy and just what we wanted (firm, pillow top) to replace our 15 year old queen Simmons that we were starting to feel the springs on. After a month, it still felt firmer that the store so we added a 2" memory foam topper (which discolored the top so now the warranty is void). After a few months we noticed there seemed to be a "hill" in the middle of the bed so we rotated it. After a couple months it seemed to get worse. We have now had this mattress over three years and will need to replace it already. The hill is now a mountain and I can't sleep more than 3-4 hours without waking up. It is the worst mattress I have ever slept on and I travel extensively and sleep in many different hotels. I will never buy a Sealy again.