Hi ComeAlongDoctor.
Welcome to our Mattress Forum! 
and thank you for your kind words. I am glad the information here is useful to you.
DF has a good shop with many quality products. The slight caution that I added is for higher weight ranges for the models that have 4lb of memory foam in the comfort layer and does not apply to the Total Latex product. Latex in general is the most durable of all the foam materials (latex foam, memory foam, polyfoam) regardless of whether it is Dunlop or Talalay or is made from natural rubber, synthetic rubber, or a blend of both. The Total Latex would be a good quality/value product with no weak links in its design.
While it can be good quality in either, synthetic, blend or all natural version … an all-natural version is often preferred because the greater elasticity that can somewhat make up for the fact that Dunlop is more difficult to make as soft as Talalay and because the lower cost of production can make up for the higher cost of using more NR latex as a raw material. NR is more expensive than SBR. Blends are often used for reasons of cost, desirable combinations of certain latex qualities, and ease of working with the material. NR is often used for its natural qualities and because it is more elastic and resilient. With the Dunlop method … NR would generally be more durable overall than a blend or synthetic (SBR) latex although there may be value in using a blend because it is less expensive and still a very durable material compared to other foams and in some cases a blend can improve the properties of the foam. In practical terms all of these differences are relatively small in the cured foam and many people would not feel significant differences between the two in side by side testing. You can see more about the differences between synthetic (SBR) and natural (NR) rubber in post #2 here .
Congratulation to Sleeper 1 on the weight loss , but I am sorry to hear that he/she is experiencing an entire range of severe chronic pains. Weight loss changes your needs and preferences in a mattress quite significantly so I am glad you are considering a component style system. 2" to 3" of latex over a 6" or 7" of support core would certainly be 'in the range" of a design or potential layering combination that could be used for a back sleeper of 215 lbs . but the type of latex and the specific ILD’s of each layer are what you will need to either sleep on or test in person to know for sure. More specific than this would depend on what your body tells you with testing on specific combinations or failing that the suggestions of the manufacturer based on their “averages” for customers that were similar to you and any other input that you could provide them to help them help you more effectively.
I know it’s one of the most common questions asked on the forum … but it’s also the question that is the least possible for anyone to know or predict for someone else. If local testing is not an option, the next best way is a more in depth conversation with each of the manufactures who have much more detailed knowledge of their specific materials and designs and would be in the best position to make suggestions that “fit the average” for their mattresses. In this case you will know how closely you come to their averages once you receive it and how much if any fine tuning needs to be done.
I am not very sure if the chronic pains Sleeper 1 is experiencing are health or mattress related, or both, bu tthis makes that much more difficult to find a best fit and you would need to identify and isolate the causes of your pains, which is not very easy. You may find helpful some of the information about the many different symptoms that people may experience on a mattress and some of the most common causes behind them in post #2 here.
I would also closely look into the pillow issue The pillow that works best can vary with different mattresses depending on how much you are sinking into the mattress and the distance between your head and neck and the mattress surface. Upper back issues can also point to a pillow that is either too high or too low for your body type or sleeping position and doesn’t maintain the gap between your head and the mattress and keep your head and neck if good alignment over the course of the night which can affect the upper back as well.
The SOL mattress also has the ability to be opened and customized… Its cover has a heavy-duty zipper that allows for layer exchanges. The zipper is hidden underneath the bottom edge of the mattress and can unzipped to access the latex foam inside the mattress and can also be completely removed and dry cleaned. You may wish to contact SOL and see if based on their experience a 6" of 34 ILD and a 3" of 30 could be better in your circumstance. I understand your concern wiht bottoming out. I would keep in mind that generally higher BMI sleepers require firmer materials (in the support layers especially). This combined with a need for a firmer surface for back sleeping indicates that you can certainly could use firmer latex. Both your finalists could be a good match depending on your needs, preferences, and both have the option to be customized before and after purchase.
Hope this helps … and I know the feeling around making the decisions about all the final details. There’s a lot to be said for gut feel once you know that all your choices are between “good” and “good”.Sometimes that’s the hardest part of all but I think that regardless of how you choose you will do well as all your options seem to be good ones and if your purchase does not turn out as well as you have hoped for you at least have a good return/exchange fail safe.
I’ll be interested in learning about your final decision and answer any other specific questions you might have.
Phoenix