Purchased a Sealy PP Matress from Kanes Furniture 2 years ago and it has begun to sag in the middle. I have serious back problems and that is why I purchased an expensive Mattress and Boxspring.
They sent out a man who took some measuements and pictures and said I would hear from Kanes the next day. Waited most of the day and then called them. They said the person responsible for making the decision would be out for several days.
He finally called and said the Mattress Sag was 1/4 inch from needing a replacement. I measured it the next morning after I awoke and the sag was almost 5/8" deep from level.
I will take some pictures in the morning and submit them to you.