Hi uptick911,
My Green Mattress is one of the members here which means that I think very highly of them and they compete well with the best in the industry in terms of quality, value, and service.
The tutorial post here has all the basic information you will need but I would make sure you do some careful testing on each mattress that you are seriously considering using the testing guidelines which will be one of the most important things you can do to make the best possible choice in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). Only you can feel what you feel on a mattress (see mattress firmness/comfort levels in post #2 here) and I would make sure you test different types of materials and mattresses to see which ones you tend to prefer.
Tim and his staff are very knowledgeable, experienced, and patient and you will be in very good hands there. Many of the members here who have bought their mattress there have spoken very highly of Tim and My Green Mattress / Quality Sleep. A forum search on Mygreenmattress (you can just click this) will bring up many of them.
Phoenix