Hi src1425,
I would make sure you know the quality of all the layers (the comfort layers are even more important than the support layers because they are generally the weak link in a mattress). The information that would be most useful or necessary is in post #4 here.
The only other advice I would give is to make sure your testing is as careful and objective as possible (using the testing guidelines), to narrow down your top choice at each store, and then finally to make some careful comparisons based on your personal value equation and all the parts of a mattress purchase (not just the mattress itself) that are most important to you.
The name of the brand is just a name on a label and what’s inside is always much more important.
Phoenix