Does this memory foam mattress need a box spring or special foundation?

Not a box spring. As an all-foam mattress it needs a solid, flat, evenly supportive base: a platform bed, slats spaced no wider than three inches, or a bunkie board over an existing frame. A sagging box spring leaves the foam unsupported and can void the warranty. Any rigid, gap-free surface works; the aim is even support so the 7-inch foam core keeps its shape.