Hi JeanieU2013,
I know you didn’t know this at the time you purchased your mattress but a mattress is only as good as the quality of the materials and construction that is used to make it and unfortunately … the major brands rely more on marketing to sell their mattresses rather than disclosing the quality of their materials. Unfortunately … even low quality materials can feel good in a showroom and for a little while after that but lower quality/density materials soften and degrade much more quickly which leads to the loss of comfort and/or support which is what is happening to you.
This foam softening is not usually covered by a warranty as you can read here because even though foam softening is the biggest reason people need to replace a mattress … it is not considered a manufacturing defect (which is the only thing warranties cover) unless the actual impressions are deeper than the warranty exclusion which rarely happens because the foam will still have enough resilience to “come back” weakly with no weight on the mattress even though they have lost much or their original properties. in almost all cases … the upper comfort layers of a mattress are its weak link because they are the most subject to repeated mechanical forces leading to softening and breakdown.
Post #2 here and post #12 here would also be well worth reading.
So what is most likely happening is that the lower quality foam that is in your mattress has softened too quickly but it still has enough resilience to come back so the impressions are less than the warranty exclusion.
When this happens … there isn’t much that can be done because to “fix” it would involve removing the foam and replacing it. Of course it’s also possible that over time your mattress may eventually develop unweighted impressions that are deep enough to qualify for warranty coverage.
There are a few possibilities that are worth investigating that may help though and they are listed in post #4 here.
If these suggestions don’t help enough to make your mattress sleepable for you … then unfortunately it may be time for a new mattress … and hopefully this time not a major brand or any mattress that doesn’t disclose the quality of the materials that are inside it.
I know that this may not be what you wanted to hear and hopefully the suggestions in the last link may help but you are in the same position as many thousands of others who have bought and continue to unknowingly buy mattresses that just don’t have the quality of materials that make them worth the price you pay.
Phoenix