There's a general complaint from most of the mattress buyers in the market, that it gets saggy when it gets little old. Many brands are not even usable after 2 years just because its "saggyness".
A sag is when the mattress is dipping down over an inch and a half, or two inches. This happens when the coil system is damaged, and doesn’t return to its normal shape. Because the issue is with the coil system, a sagging bed will not provide correct support, and will not ever return back to normal. The great news is that if this happens to you, your warranty kicks in and chances are you’ll get a new bed.
A body impression is a slight depression of the foam on the top of the mattress. If you think logically about the components of a bed, it’s just common sense that this would happen. You are putting your whole body weight in the same spot for eight hours a day for ten years. Foams will compress and mold to your curves, especially with this type of wear. Your shoes become more comfortable when they’ve formed to the bottom of your foot, and your couch would surely develop an imprint if you sat in the same spot for eight hours a day, every day. To expect your mattress’s foam to maintain its loft is unrealistic. Body impressions don’t change the support of the mattress, nor do they drastically change the feel; they are a normal part of the wear of the mattress.
Here’s the key to reducing body impressions: the more padding that’s on the bed, the bigger the chance that body impressions will form. The less padding, the less that these foams will compress, and the less likely that a body impression will show. Does this mean that you need to sleep on something that’s hard as a rock? No, of course not.
You can get a mattress that has a medium amount of padding on the top, but that has a more conforming coil system, like a Microcoil® Mattress by Snooze Sleep. Microcoil® have individually pocketed coils, and they contour to your curves so the padding isn’t doing all the cushioning, and you’ll need less of it to be comfortable.
Another option is to make the move to memory foam or latex. These specialty foam beds don’t have the body impression problems like regular foams do, since they are much denser and more resilient. Even if you don’t want to buy an all foam mattress, you can find innerspring beds that have memory foam or latex in the padding layers, like AntiIGel® Mattress and Latex® Natural Mattress.
The bottom line is that body impressions are normal, and they will happen to every bed, regardless of how much you pay for it. It does not change the feel, the support, or the life of the mattress.
However, if the problem is deeper than just the compression of the padding, a warranty claim might be in order, to make sure that you’re getting the correct support that you need.