Hi mnguy,
You may be confusing a box spring with a foundation. A box spring is a mattress support system with springs inside it that flex and a foundation is meant to be a rigid support surface that has little to no flex (and could have a solid surface or a surface with rigid slats or a wire grid).
A memory foam mattress usually does best with a rigid non flexing foundation or platform bed that has an evenly supportive surface that doesn’t flex under the mattress. There is more about the different types of support systems and which ones tend to work best with different types of mattresses in the foundation sticky post here and the two other posts it links to in the second paragraph.
You can see my thoughts about a solid surface vs a rigid slatted surface in post #10 here.
Tempurpedic is the most common memory foam mattress and their foundation has a solid surface. A google search on Tempurpedic mold will bring up examples of mold issues although there were probably other risk factors involved as well.
Phoenix