Hi Cindypri,
the first place to start your mattress research is post #1 here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and avoid the worst ones.
You are fortunate to live in the Phoenix area because you have more high quality/value options than most areas of the country which includes three of the members of this site. The better options in the area I’m aware of are listed in post #4 here.
Phoenix