Hi Psyotik,
Post #2 here includes some of the better possibilities in and around Jackson.
It’s not likely that any of them will have the same quality/value as the online outlets you already know about but they can provide good testing grounds that can help you narrow down your preferences in materials and the best choice for an online order. If in the course of your local testing you come across similar value as an “exception” (such as a clearance or other particularly good value) … then so much the better.
Just make sure that if you want to use a particular mattress as a guideline that either the outlet can and will provide you with the layering or it is available online so that you can compare it to similar materials and layering that are available online.
Phoenix