We just bought new waterbed mattresses. Two years ago we paid a lot of money for a top of the line Sealy mattress and within three months it was forming what my husband calls - nests. Where our body weight is the heaviest, the mattress sank. We turned it around and head to bottom and all that happened were more "nests."
I had three back surgeries last year and this thing hurts me.
So the waterbed mattress has two sections for comfort control, lumbar support, and other features for the individual. Not to leave out, temperature control. Warm sheets in the winter and cool in the summer.