What foundation or box spring does this mattress need?

Use a firm, flat, fully supportive base rather than a springy traditional box spring. A solid platform, a slatted frame with slat gaps under 3 inches, or a low-profile box foundation all suit it, and it is adjustable-base compatible too. Even support keeps the 1050-coil 3-zone system level so the firm surface stays true, and it protects the 10-year warranty, which a sagging or unsupportive base can void. Pair it with a sturdy frame given its 13-inch height.