Hi sbidaho,
Hopefully you’ve read post #1 here and are following the steps.
If you are “stuck” on step 3 … then some of the better options I’m aware of that are reasonably close to you are in post #9 here.
As the guidelines suggest … I would avoid any mattress where you aren’t able to find out the quality of all the layers which are inside it (including the spring Air you linked which has far to much “mystery foam” in the layering) and would be a risky and “blind” purchase unless you know the density of all the foam layers. With Spring Air … this isn’t something you will likely be able to find (see this article).
Regardless of how soft it may be … when you have that much lower quality materials in the upper layers of a mattress (over 3 1/2" in this case) then the risk of foam softening and the more rapid loss of comfort and support that goes with it is much higher. Foam softening and the breakdown of lower quality materials in the upper layers is the main reason that people need to replace a mattress and isn’t covered by any warranty except in the rare cases that the resulting unweighted impression is deeper than the warranty exclusion and there are no other warranty exclusions that apply to you.
Phoenix