Hi Mstrlucky74,
Any rigid evenly supportive support surface would be fine including a foundation or a platform bed where the gaps were close enough together to prevent the mattress from sagging into the gaps would be fine. I wouldn’t use a box spring (a box spring has springs that flex under the mattress and generally aren’t the best choice with a foam mattress). They will give you more specific information about the types of foundation that they suggest when you talk with them. There is more about foundations and mattress support systems in the foundation post here.
Yes … they are on the CertiPur list here*.
ADMIN NOTE: *Removed 404 link|Archived Footprint: certipur.us/pages/for-consumers/find-products/
I think you may be mixing up the definition of HR polyfoam with the guidelines for polyfoam density that are suitable for use in a mattress. The density guidelines I would suggest are in post #4 here.
Comfort layers are the upper part of a mattress that is primarily meant to provide comfort and pressure relief. Support layers are the deeper layers or components of a mattress that are meant to primarily provide support/alignment. The middle layers are transition layers that have a dual function and help with both. There is more detailed information in post #2 here.
Phoenix