Hi pmblood:
Phoenix has some great advice from a similar question to yours in Post #2 here that you might find helpful.
While your age certainly may have some culpability to your morning soreness, you certainly will be able to benefit from a new mattress with yours being 24 years old. Soreness that goes away during the day is often a sign that your comfort layers have stopped being comfortable 
. Being a side and back sleeper, be sure that whatever you choose allows for a decent level of conformation (with decent being based upon your personal opinion, of course).
Here’s a list of dealers in the Salt Lake City area in Post #2.
Good luck!