Hi lilac,
The manufacturer is always the most reliable source of information about the box spring or foundation it was designed for since they are the ones who designed the mattress and this is always the first “rule” of choosing a foundation as you can see in the foundation post here which says in the third paragraph …
This has nothing to do with whether a manufacturer is a member here or not but if you believe that you are more knowledgeable than the manufacturer that designed and manufactured your mattress then of course you are always free to choose whatever you believe.
The reality is that if you have tested a box spring with your specific mattress and it works better for you on any particular mattress in terms of PPP and you are happy with spending the additional money on purchasing the box spring then that would be the best choice for you regardless of whether it would be the best choice for anyone else and purchasing a box spring is certainly an option that is still available to you.
Phoenix