Hi frickinfractals,
You can see my thoughts about a wire grid foundation in post #10 here.
They have had good success with the frame/foundation and you certainly won’t have any issues with the foundation sagging because it is very strong but if you are at all concerned with the spacing between the wires over the longer term (out of “an abundance of caution”) then you can also add something like a bed rug in between the foundation and your mattress.
Phoenix