Hi BigBlueinll,
The first place to start your research is the tutorial post here which has all the basic information, steps, and guidelines you will need to make the best possible choices.
The minimum quality guidelines I would use for a memory foam mattress are in post #10 here.
The better options and possibilities I’m aware of in the Chicago area are listed in posts #2 and #4 here and I would make sure you visit Quality Sleep / My Green Mattress which are members of this site and compete well with the best in the industry in terms of quality and value.
Phoenix