Hi Doubleight,
Let me dive right into your questions.
Starting with local stores as you have is great. Driving a little further could also be worth your while. I would search on google in your surrounding area and visit another location or two that carries a potential type of mattress you are considering. You can then use TMU by typing in a “key term” in the Forum Search in a city or area you live close to and see what businesses have previously been discussed in that area that could be helpful for your search. Once you have a business or a few you are considering, you can read this article to confirm that the retailer or manufacturer is transparent with their products and meets Post #13 quality/value guidelines here. Local testing will first help you get a clearer sense of different materials and layering and also determine your needs and preferences. This coupled with your sleeper stats as you previously mentioned regarding body type, sleeping style etc. will help to make a good purchase.
This is why TMU is a great resource since they not only provide so much knowledge and information, but they have their Trusted Members who are all highly ranked and valued. A lot of these companies have a reasonable exchange/return in place and allow the customer to rearrange layers according to comfort needs. Most of these online manufacturers are very good at what they do, helpful, and can be fairly accurate with their recommendation for you. The more specific and detailed the information you provide to them, the better they will be able to help you make the best possible choice from the options they have available. Hopefully you would easily be put in touch with the correct person to have a conversation and get their recommendation. Press “0” if you have some difficulty to get directly in contact to a representative or call again later. Once you get a rep on the line, make sure you get all your questions answered! I think all the Trusted Members on TMU should be very responsive and much more consumer friendly than a typical Bed in the Box.
Post #2 here has information about the different ways to buy a mattress (locally or online) that will be the best “match” for your preferences, body type and sleeping positions, and can help you to minimize the risks involved. You can also follow the steps outlined in the mattress shopping tutorial here. If a mattress is a good match for you in terms of PPP keep in mind that a mattress is only as good as the quality of the materials inside. This article will help determine the quality and whether it has any weak links in terms of durability.
In conclusion, search for local retailers, compare those to this site, find a few to go out and test, inquire and learn about the quality of the materials inside, know your preferences and stats, use the articles listed above to learn about the quality/durability of the materials, browse the trusted members on this site, then use all of this information to have a more detailed Q&A with a retailer or online manufacturer. These steps will help to determine your preference and will also educate yourself regarding the different companies and products/options they offer. Layer exchange programs or a return policy may be an important part of your personal value equation should you choose to go with an online mattress.
Best of luck! 
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