Stick with the big stores

We had had multiple mattresses from this store and have had problems with all of them. The first time, we returned the mattress and upgraded to better one but still had the problem the mattress sagged within months. Then we again replaced the entire set and rebought 2 twin XLs instead of the 1 king and still had the problem. My husband, whose mattress is the one that sags is not overweight.