Hi Lauren.mixon,
LEW has already mentioned the first suggestion I would have (and some other very valid points as well) which is to start with local testing using the information, guidelines, and steps in post #1 here. In many cases and depending on where you are the local value can be as good or sometimes even better than online options but of course this would also depend on your own personal value equation. Either way … I think local testing of the materials and types of mattress you are most interested in (or to find out which materials and designs you tend to prefer) is important part of any purchase no matter where you end up buying.
Post #2 here and post #2 here and this thread about the pros and cons of online vs local would also be worth reading.
Phoenix