My prior Serta Perfect Sleeper lasted more than 20 years, and was only replaced because it was too big. I shopped mattresses online for weeks before deciding on the Serta Perfect Sleeper Kleinmon II Firm. First of all, if it has a layer of "cooling gel," as advertised, it doesn't work. This is the hottest mattress I've ever slept on. Second, it's lumpy, even through 2 mattress covers. Third, and most important, this mattress developed a deep sag in the middle before it was even 6 months old. I sleep in this bed by myself and tend to sleep on one side of it - not even in the middle! I'm very disappointed in this Serta, but can't afford to replace it.