Hi thomas2929,
You can read a little more of my thoughts about buying from Costco in post #4 here and more about sleep Science in post #2 here.
A mattress is only as good as the quality of its construction and materials and they don’t list the quality of the memory foam or the polyfoam layers. Without this there is no way to make a meaningful assessment of a mattress. If you look at the old Southbay site here though you will see that the Emma uses 3" of 3 lb memory foam and 2" of 1.5 lb polyfoam underneath that which would both be too low quality/density for me to consider. They are also not CertiPur certified which is one of the criteria I use for all Chinese memory foam mattresses so they don’t meet the guidelines I use in terms of CertiPur and foam quality so I would tend to avoid them.
Some of the better options I’m aware of in the San Luis Obispo area are listed in post #2 here and some of the better online memory foam options I know of are listed in post #12 here.
Just in case you haven’t read it … post #1 here is always the best place to start your mattress research.
Phoenix