Hi Leobuck1,
Outside of an online purchase … the only place that carries the Select Foam Mattresses is Brickell Mattress which is their bricks and mortar store in Miami.
You can read more about “soy based” polyfoam in post #2 here. I would treat them the same as regular polyfoam in terms of quality/density so you can make meaningful comparisons based on density.
You can also read more about some of the many different types of gel memory foams and some of the differences between them in post #2 here and the links it includes. Again though … in terms of quality/durability you can make meaningful quality/durabilty comparisons between gel memory foam and regular memory foam based on the density of the foam although all the different types of memory foam (gel or otherwise) can have a different “feel” and response depending on their chemical formulation.
Phoenix