Hi eopandabear,
They may have more options available than you realize (or that you tested). The firmness of the support layer and the comfort layer as well as the thickness of the comfort layer will all affect the feel and performance of the mattress so if all they had was two different firmness options in their support core and two firmness options available in their comfort layer then with the two different thicknesses of comfort layers that would give you 8 different options to try that are each different from each other. One of these would generally be a good match for the majority of body types and sleeping positions.
I understand the “overwhelm” that can come from having too many options but I would focus on their 9" and 12" models. For most people 8" to 9" would be in the range that would be suitable for most people while 12" would be a good option for higher body weights or a preference choice for people who preferred a thicker mattress (see post #14 here about mattress thickness). I agree that outside of those who for preferred the “feel” of a thicker mattress for some reason and where none of the configurations of a thinner design worked as well … 15" would be thicker than most people would choose or need.
You are certainly looking at some good quality/value latex options.
Phoenix