Hi Lana,
There is more about the most important parts of the “value” of a mattress purchase in post #13 here that should be helpful when you are comparing mattresses.
Outside of careful testing for PPP (Posture and alignment, Pressure relief, and Personal preferences), the most important part of the value of a mattress is knowing the type and quality of all the materials and layers inside it (see this article).
Only your own testing or experience can tell you which of the mattresses you are considering is the best match for you in terms of PPP (see mattress firmness/comfort levels in post #2 here) but I can certainly make some comments about the quality of the materials or help you identify any weak links in the designs.
You will be able to tell which of these are correct by matching them with the thickness of the mattress. You can also check the law tag to make sure that the mattress you are looking at only contains latex.
Either way … all of the materials are high quality (blended Talalay latex) and there are no weak links in either version. Having said that … If the first version is correct then this would have very soft comfort layers which can be somewhat risky for some people in terms of alignment so I would make sure that your testing confirms that you are in good alignment in all your sleeping positions on this mattress.
The Marriott Foam core is 1.8 lb polyfoam and this is a good quality material so in combination with the latex comfort layers in both of these mattresses there are no obvious weak links in either of these.
I would be cautious with this mattress because the specs you listed contain more than “about an inch or so” of unknown materials in the description and without more specific information it’s not possible to make any meaningful comments about either one of these mattresses. If you can find out the density of all the polyfoam in the comfort and quilting layers then you can compare them to the guidelines here or if you list them on the forum then I’d be happy to make some comments about it as well.
Based on the specs you listed there is only 2" in total of either less durable materials (the polyester fiber) or unknown materials (the 1" super soft polyfoam used in the quilting layer) and the other layers are all good quality (talalay latex, a microcoil and the Marriott foam core) so this would be “on the edge” in terms of having a weak link in the design although it would be less risky in terms of durability than the St Simons.
Phoenix