Hi Cozycamper,
A floor model in the store will usually be softer than a brand new mattress which hasn’t had a chance to break in yet but this could also be the result of more “subjective” testing in the managed environment of many mattress showrooms. It’s not unusual at all that if you test only for a subjective sense of “comfort” in a store and have tested other mattresses in the same way either before or afterwards … that the mattress can feel very different at home (or even the next day or hours later in the same store) from what you remember.
So the first step is to make sure you have gone through any adjustment period (your body will need to adjust to a new sleeping surface that is different from what it is used to and this can take a few weeks) and that the mattress has a chance to go through its initial softening and break in period. How long have you been sleeping on it?
If it seems clear to you that things are getting worse instead of better and the adjustment period is going in the wrong direction … then it’s quite possible that you have chosen a mattress that isn’t suitable for your body type and sleeping style in which case it’s not likely to get any better.
It’s not unusual that there are no returns and only exchanges but unfortunately this means in many cases that you may not have the choice of any good quality/value mattress to exchange for and there could be some hidden costs involved as well.
Post #66 here and the other threads it links to has some discussions with other forum members that were in a similar situation and needed to make the best of a bad situation and some of the options that were available to them.
I would also read post #1 here and the information it links to which will give you the basic information you will need about mattresses, the materials in them, and testing more objectively to be able to make more meaningful comparisons between the options you have.
If you let me know which store you purchased from I can scan the mattresses they have and may be able to point you in the direction of any better “value” they may have there.
Phoenix