Hi sweatdog,
I’m not quite clear on what you mean here. You would only need to use a foundation or a box spring … not both. A foundation or box spring would be placed on a bedframe (either steel or wood) or in some cases can be used with legs that raise them off the ground. I would make sure that in a full size or better that your bedframe has good center support to the floor with at least 1 but preferably 2 or more legs under the center support.
If your bedframe needs additional cross members to strengthen it so it can properly support a foundation or box spring or needs better center support to the floor then something like these or something like these may be helpful and you can also make T-Slats like this to prevent wooden slats from bending or sagging and post #12 here also has some suggestions for center support legs that can be used under a foundation or bedframe.
Phoenix