Hi puppylover,
Welcome to the Mattress Forum! 
Since you’ve been looking on the site already, the first thing you need to do I make sure you’ve familiarized yourself with the mattress shopping tutorial .
The simplest version of the tutorial boils down to FIRST finding a few knowledgeable and transparent retailers and/or manufacturers that sell the types of mattresses (see this article ) that you are most interested in (either locally or online) and that can provide you with all the information you need to know to make an informed choice and make meaningful comparisons between mattresses and then …
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Careful testing (hopefully using the testing guidelines in this tutorial) to make sure that a mattress is a good match for you in terms of “comfort”, firmness, and PPP … and/or that you are comfortable with the options you have available to return, exchange, or “fine tune” the mattress and any costs involved if you can’t test a mattress in person or aren’t confident that your mattress is a suitable choice.
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Checking to make sure that there are no lower quality materials or weak links in a mattress you are considering relative to your weight/BMI range that could compromise the durability and useful life of the mattress (see the durability guidelines here)
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Comparing your finalists for “value” based on #1 and #2 and all the other parts of yourpersonal value equation that are most important to you.
If you can’t find any local retailers with products that meet your demands, then I would look online and use the experience and expertise of the members listed in this post who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex, memory foam and other options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
Their detailed knowledge of their mattresses and how they fit with different body types and sleeping positions along with your feedback from local testing, a customer base of many people that they can use as reference points, and any exchange, return, or any options they have available to customize a mattress after a purchase can help lower the risk of an online purchase. These online retailers or manufacturers can also be a good “value reference” for local purchases to make sure that if you are paying a “premium” for a local purchase (in exchange for the kind of “in person” guidance, service, and value that comes with dealing with a local retailer that can help you make more “accurate” choices that you have tested in person) is not too high.
This post here and this topic have more about the pros and cons of a local vs an online purchase.
If you reply with your zip code I can see if I have any potential dealers for you to research in your area.
Phoenix