Hi krupnik4,
In case you haven’t read it already the first place I would start your research is post #1 here which has all the basic information, steps, and guidelines that can help you make the best possible mattress choice.
Sleep Science (from top to bottom):
3" of natural latex (listed as Talalay but ILD and blend unknown). This is probably blended Talalay.
6" of natural latex (listed as Talalay but ILD and blend unknown). This is probably blended Talalay as well.
Wool quilted cover.
Although I would want to confirm the blend and ILD of the latex … these are all good quality materials with no obvious weak links in the mattress.
Nature’s Caress (from top to bottom):
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1" super soft polyfoam (density unknown)
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2" 24 ILD latex (type and blend unknown). The ILD rating suggests Talalay because this is one of the ILD ratings for Latex International blended Talalay but it may also be Dunlop which may feel firmer than the ILD indicates
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6" 32 ILD latex (type and blend unknown). Same comments about the type.
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2" 40 ILD latex (type and blend unknown). Same comments about the type.
7/8" firm polyfoam (density unknown)
Knit cotton cover.
I would want to confirm the type and blend of latex here but the ILD’s suggest that it is blended Talalay. Regardless of the type there are no obvious weak links in this mattress either in terms of the quality of the materials. The polyfoam in the quilting layer is within the guidelines I use of “around an inch or so” and the polyfoam layer in the bottom is a stabilization layer which would not affect the durability of the mattress. overall this would be a good quality choice.
Other than this both of these would be somewhat of a risky purchase because there is no way to test the mattresses ahead of time. Costco has little knowledge of mattresses and are not the best source of guidance about the suitability of a mattress in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). The firm side of the Nature’s Caress would be too firm for most people but the soft side is “in the range” of a suitable choice that “on average” would work for some people. The Sleep Science is completely unknown.
In terms of value they both have fewer comfort options (both with your purchase and after your purchase) and are more costly than other choices that are available to you from online manufacturers that have more flexible options and better prices and value.
You can see some of my thoughts about buying from Costco in post #4 here. They do have a good return policy so you do get a free “roll of the dice” but so do many of the manufacturers that are members of this site that have better options, better value, and also sell online so this is not really a significant advantage for buying from Costco in this case.
While both mattresses from Costco are fair value (especially compared to other mainstream mattresses) … your local options in the Phoenix area would give you much more flexible and customized and better value choices that you could actually test ahead of time.
Phoenix