Hi arearcher,
Welcome to the Mattress Forum! 
Picking out a particular mattress isn’t something that I can do for you, but I can certainly help with “how” to choose a mattress.
It sounds as if you’ve already done some reading on the site, but just in case you haven’t read it yet, the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Regarding value…there is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and 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).
While price is certainly important of course … the “value” of a mattress purchase is what is most important and price is just one of many factors that can affect the “value” of a mattress purchase. There isn’t a “formula” that can be used to assess or “calculate” the value of a mattress because there are so many different variables and criteria involved that can affect the price of a mattress that can each be more or less important to some people and not to others who may have completely different criteria or definitions of “value”. The value of a mattress purchase is also relative to how a mattress compares to the other finalists you are considering or to other mattresses that are available to you in your area (or online if you are also considering online options). There are many reasons that a mattress that may be “good value” for one person or in one area of the country may not be good value for someone else that has very different needs and preferences or that lives in a different area.
Regarding the Therapedic Natural Splendor, I would confirm those specifications with the actual retailer, as Therapedic has different licensees throughout the country and each licensee has the latitude to produce different variations upon a theme, and the specifications listed on Therapedic’s web site or provided by Therapedic “corporate” don’t always match up with what a licensee is producing. The specifications you linked to are three years old and are for what was called the Natural Splendor II, and I personally don’t know that these are the same specifications of the mattress you tested locally. In the specifications you provided, there is a total of 6" of Talalay latex (blend not mentioned), under which are two layers of 1.8 lb polyfoam. This would be good componentry and generally not a cause for concern for someone in your BMI range.
SleepEZ is a member of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration. Their latex mattresses are all-latex, and for a similar price to the Therapedic you could have a mattress using more overall latex and the ability to customize layers for different comforts, even on the left and right side.
If you are considering looking online, a good place for you to start could be to use the experience and expertise of the members listed in post #21 here 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 options included in the choices and I think highly of the advice that these companies provide.
While other people’s comments about the knowledge and service of a particular business can certainly be very helpful … I would always keep in mind that you are the only one that can feel what you feel on a mattress and I would be cautious about using anyone else’s suggestions, experiences or reviews on a specific mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how you will feel on the same mattress or how suitable or how durable a mattress may be for you. In many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person or even a larger group of people in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) may be completely unsuitable for someone else to sleep on (even if they are in a similar weight range). In other words … reviews or other people’s experiences in general won’t tell you much if anything about the suitability, quality, durability, or “value” of a mattress for any particular person (see post #13 here).
I see you’ve already found the listing of some of the Boston-area retailers who might offer some better options for you to sample. And Spindle would also be an excellent choice for you to consider. They are also a site member here, and are very knowledgeable about latex, and their mattresses would offer you more overall latex than the Therapedic model you are considering.
I’ll be interested in learning how your shopping experience proceeds.
Phoenix