Hi Cyd,
[quote]“premium Layers”. (Comfort layers?)
The latex is .5 Talalay (BTW: Can you give me an idea as to how that word is pronounced? Which syllable is accented?)
Then .75 CertiPUR-US Comfort foam (seems rather vague!)
.5 Gel infused Memory Foam
Support Core
7" CertiPUR-US Certified Plant Based Foam (uh, what plant!?)
1.5 Stabilizer Foam (again, really vague)[/quote]
Most of this information has little meaning and what you need to evaluate a mattress is the thickness of the layers along with the foam density in the case of polyfoam or memory foam and the type and blend of any latex. The only part of this that they disclose is the talalay latex (which is a good quality material and probably blended) and the thickness of the 1/2 gel memory foam layer (again with no density information).
The latex in this mattress is only 1/2" so it’s more for label copy than anything else.
Besides the latex and gel memory foam, the rest of the foam materials in the mattress would probably be polyfoam (the comfort foam, the “plant based” foam, and the “stabilizer” foam) and the density of each of these layers is the single most important factor in evaluating their quality and durability.
In most cases … Spring Air is one of the major brands I would tend to avoid because they don’t disclose the information you need to make an informed choice or meaningful comparisons. When you are able to find out (usually through “alternative sources” or some frustrating research that usually leads to dead ends) you will usually discover that the quality/density of the materials is lower than many other mattresses with better quality and value. As you can see in the guidelines here … I would avoid buying any mattress where you aren’t able to find out the information you need about the quality of the materials inside it.
You can read a little more about “soy foam” or other so called plant based polyfoam or memory foam materials in post #2 here. They are just a version of polyfoam or memory foam and the density can be directly compared to “non plant based” foams.
You can also read more of my thoughts about buying from Costco in post #4 here.
Talalay is pronounced tah lah lay with the emphasis on the first syllable (you can hear it pronounced here)
Hope that helps 
Phoenix