Hi Csj0952.
Thank you for your appreciation! 
I am glad that Jamestown Mattress worked with you so closely, I think highly of them and the quality/value of the mattresses they make compared to most other manufacturers, I also understand why you would want to go with option 1 and accept the refund, the good news is that you clearly know much more about your needs and preferences, materials and quality/value equation than most.
Either method has advantages so you would need to weigh them according to all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for) to see what makes best sense for you. Post #2 here also has more about the different ways to buy a suitable mattress (either locally or online) that is the best “match” for your body type, sleeping positions, and preferences that can help you assess and minimize the risks involved in each of them. When choosing something online, it’s important to deal with experienced, educated and helpful manufacturers who have the knowledge to guide you through the process and find something that they honestly think will fit your specific sleeping positions, somatotype, BMI and individual needs. Post #2 here and this topic have more about the pros and cons of a local vs an online purchase.
Regarding the zoning that you are considering again, there is no consensus that 5 zones are better than 3, or that ANY ZONES are better than NONE. It is much better to deal with an experienced manufacturer with such products instead of guesses and suppositions and of course again when it comes to such fine-tuning you would be better served to try things out in person.
1"-2" for a prone sleeper is a general guideline for the “quilt” layer of a mattress or the uppermost layers. There would usually be deeper upholstery layers beneath that. Also keep in mind that these are guidelines and not absolutes and especially with your back pain the better approach would be to use your past experiences and go from there with what did and didn’t work so far. I agree that always conversations with the manufacturer to clarify any of your concerns would be the best way to move forward as they would know best their materials and designs and how these would work for people that are similar to you. If you know enough now to do
everything “right” in terms of the process the and “risk management” which is the best you can do if you chose to go with an online mattress purchase.
I hope this gives you a good way to move forward and once you have a chance to narrow down your options please let me or any of our Expert Members know and if you have more specific questions we’ll be happy to assist you.
Phoenix