Hi bbmouse,
I’m sorry to hear about your circumstances and unfortunately you are in a similar position to many other members that have come here after buying a major brand mattress and have been “caught in between a rock and a hard place” where you don’t have any great options available to you.
While it’s possible that you ordered the wrong mattress (you could check the law tag to make sure) or that you have a defective mattress (which would be a warranty issue if any visible impressions are more than the warranty exclusions) … the most likely possibility is that the issues you are experiencing are connected to the use of lower quality materials in the comfort layers that have softened enough that you have crossed over the threshold between sleeping well on a mattress and sleeping on a mattress that is no longer a suitable match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). Unfortunately the loss of comfort and support that is the result of foam softening isn’t covered by mattress warranties (see post #174 here). This can happen quite quickly if the mattress was already “on the edge” of being too soft for you when it was new so that even a relatively small amount of softening could take you over the edge (see post #2 here).
There are some suggestions in post #4 here that may be helpful (and I would make sure that the support system isn’t contributing to your issues by sleeping on the mattress on the floor) but if a mattress has soft spots, is sagging, or is too soft, then a topper would generally be a partial or temporary solution at best and at worst could make the issues worse because a topper will just follow the soft spots or layers underneath it.
If the cause of your issues are the mattress itself then post #2 here has some strategies and suggestions that you can use to make the best possible exchange and help you make the best out of a difficult situation.
Phoenix