Hi Benstark,
There is more about metal bedframes in post #10 here but if it isn’t one of the cheapest ones and has 1.5" angle iron and a center beam with good center support to the floor (preferably with two legs in the center) then it will probably be fine.
I don’t know the specifics of the box spring you have (or whether it is a box spring that has springs inside it that flex or is a foundation that has a rigid support surface with minimal or no flex at all) but there is more information about the types of support systems that are generally best for different types of mattresses in the foundation post here. Foam mattresses generally do best with a rigid, evenly supportive, and non flexing support surface so if you have a foundation that is still in very good condition and has little to no flex and still has a flat support surface and there is no sagging or weak spots anywhere on the surface of the foundation when you test it with strong compression (with your knee) then it should be fine.
Post #2 here should be helpful if you need to dispose of or recycle an old mattress.
Phoenix