Hi PackerBackerCH,
Taking time to get used to any new mattress is normal, especially if you are changing to componentry with which you may not be familiar. There will be a break in and adjustment period for any new mattress or sleeping system as the mattress loses any of it’s “false firmness” and the cover stretches and loosens a little, and your body gets used to a sleeping surface that is different from what it is used to and loses some of its “learned alignment” (see post #3 here). This would typically be 2-4 weeks, but it can be shorter or longer depending on the specifics of the person and the mattress.
The TitanFlex comfort material used in the BB Signature is very point elastic, so that may also be a difference as compared to your old mattress. The good news is that if you do eventually decide you need to make a change, you did have the foresight to choose something that has a good return/exchange policy.
Phoenix