The mattress is horrible

Our mattress is now about 4 years old. At first we loved it. But as time went on it got worse and worse. It was the top of the line Bemco Memory Foam. Now every night we climb into bed it sinks down many inches. If you get up to go to the bathroom you have to climb out of the hole and when you come back you climb back down in, because it has not raised back up. We are not fat. My husband weighs 172 and I weigh 135. I am so dissapointed I can not even think of the words to say. When we got rid of our old mattress (that was 2 years past it's warranty) it was mostly flat and no holes to get in. This one shows sunk in places on both sides through the bedspread, blanket and sheet. When we purchased it they "compared" it to a Tempurpedic Classic. My son has one and it has no holes after 8-9 years. You would think when a mattress costs over $1200 before tax it should last a while!!