Hi Nene1957,
There is more information about support systems (bedframes and foundations or platform beds) that are generally suitable for different types of mattresses in post #1 here and some of the information and comments in this topic (which would apply to any foam mattress) may be helpful as well.
The height of a support system is just a preference choice that will affect the height of your sleeping surface and outside of your own preferences one height isn’t any better or worse than another.
If you add up the height of all the support components you would be using under your mattress (bedframe and foundation) and then add the thickness of the mattress you would have the height of your sleeping surface and you can compare it to your current mattress and support system (or others that you are familiar with) as a reference point and decide if you would prefer something that is the same or lower or higher.
If your current foundation meets the criteria for your mattress in the reference post I linked and there is no sagging, flexing, or weak areas and it provides a flat and rigid support surface and has good center support to the floor then it would probably be fine. If there is any flexing or sagging or bowing or weak areas in the support surface then it would be a good idea to replace it.
You may have found this already but the main pillow topic here and the topics it links to should be helpful.
Phoenix