After a few months we have mixed feelings about th...

After a few months we have mixed feelings about the Comfort De Luxe koudschuim model we bought. We really liked it in the beginning, but now my husband thinks it lost part of its firmness exactly in the area where he's sleeping. About 3 months ago we switched sides and now it seems the side he moved to is starting to have the same issue. He weighs 90kg and the mattress is the firm model which should be able to handle more than 100kg.
Maybe our expectation that, even as time passes, you wouldn't notice the area of the mattress that is slept on was unrealistic. Perhaps it's impossible for a place used for 8 hours a night to remain just as firm as the edges of the mattress that rarely receive pressure.