Hi lotus65,
Unfortunately this is far too common in the industry with mattresses that use lower quality foams in the comfort layers where the foam softens and breaks down (without visual impressions) much too quickly. It’s one of the reasons I would always make sure you know the quality/density of all the foam in a mattress and I would also avoid the major manufacturers who either won’t disclose this information or who use lower quality materials than many other smaller more independent manufacturers.
The impressions would also need to be “unweighted” after the foam has had the chance to recover which is the one reason that so many warranty claims are rejected. There are also other exclusions in most warranties (such as even a small stain on a mattress) which will void a warranty. There is more about warranties in post #174 here. “Virtual impressions” and the loss of comfort and support due to foam softening is not considered to be a defect that is covered by a warranty unless it’s deeper than the warranty exclusion … even if it means that the mattress needs to be replaced.
While there are no “good” options for a mattress that has soft spots or is sagging … post #4 here has a few suggestions that may be helpful … at least on a partial or temporary basis.
That’s good advice … and I would also expand on it to include all the largest manufacturers or any mattress where you can’t confirm the quality of the comfort layers in the mattress.
Phoenix