Hi TxFox,
I think the first step when you are reaching a point of “information overload” is to put your research efforts into connecting with the best manufacturers, outlets, and people rather than finding the best mattress. In your case … there are some good options (including several that make or carry latex mattresses) in the Houston area in post #2 here. This way you only need to know enough to be able to tell who knows what they are talking about and you can trust instead of needing to learn all the complexities yourself and your efforts can go into testing rather than analysis.
I also like the feel of the Terra a lot. It is a soft latex mattress (and I like soft :)) and is great quality. Of course as you mentioned I would never consider it at the prices they charge when there are others that are roughly comparable that are so much better value. I’m not sure I should take the “risk” of focusing you more on specs like ILD but since the information is available … there is more about the Terra in post #6 here.
Mattress layering can be very counterintuitive and different people will also feel the same mattress differently depending on what they focus on the most and the layers (and areas of the mattress) that affect their perceptions the most. Sometimes seemingly less important details (like thicker layers of wool) can make a bigger difference than many people would suspect. It can take a lot of endless “analysis” to explain these differences but all of this can be bypassed if you are working with a knowledgeable and experienced manufacturer or sleep shop that has good quality and value mattresses available in the materials that you prefer.
Even with a material as durable as latex … having a two sided mattress is a “value bonus”. Other good options can be replaceable layers with a zip cover or having a local manufacturer nearby that can open up the mattress and change out a layer if one softens or wears out before the rest.
Organic is really a certification or a “process” standard rather than a “quality” standard. In other words it “certifies” that a product or material uses ingredients that were grown, produced, or manufactured using organic methods but the same material that doesn’t go through the organic certification process may be basically the same … except it isn’t certified. There is more about blended, natural, and organic in post #6 here. There is also more about the different types of latex in this article.
Outside of latex which is an excellent choice for your type of environment (it resists dust mites which is a leading cause of allergies and is breathable so it helps to control humidity in the mattress), I would focus on using highly breathable layers throughout your sleeping system. This means natural fibers in the cover and quilting layers (such as organic cotton/wool combinations) and in your mattress protector (the dormier wool protector would be a great choice) and in your bedding as well (high quality cotton such as Egyptian or Pima, bamboo, or linen (flax) would be good choices). It would also be important to use a slatted foundation. This way there are no “barriers” to overall ventilation of your mattress. Again though … a good manufacturer or retailer will know all this and give you good guidance.
Savvy Rest is a high quality manufacturer but they are very expensive compared to other manufacturers that use the same or similar materials and have the same benefits (such as some of the online manufacturers that are members of the site listed in post #21 here). There are many mentions of them on the forum and a search on Savvy Rest will bring up lots of posts and comparisons.
There is some “history” with Green Mattress Factory and before you consider them I would do a few hours of reading and research online to make sure you were comfortable with some of their past. You can start with some of the links in post #6 here.
My Green Mattress is one of the members of this site and are listed in the link I gave for online members. They and the other members here have some of the best quality, service, and value in the country and I think very highly of them…
As you mentioned … this is not really possible to quantify or predict because the reasons that a material softens has many variables and can’t be predicted on an individual level. there is more about this in post #2 here. Depending on where inside the range of your needs and preferences your mattress falls … different people will be affected differently by softening. For example if someone were to buy a mattress that was on the verge of being too soft for good alignment, then even a minimal amount of softening over the first few months could put them over the edge and their mattress may no longer be suitable. Latex though will soften less than other materials and if you choose a mattress that is not “on the edge” of the range of your pressure relief and alignment needs … then this shouldn’t be an issue. A good guideline is “just enough” softness and not more. Some manufacturers also offer a side to side split which means that each side of a mattress can be built differently for couples of differing needs and preferences although there are other ways to accomplish this as well.
If I was in your shoes … I would step back from “analysis” and my next step would be to talk with some of the better choices in the Houston area and then visit the ones that you best “connect” with.
Phoenix