Does this foam mattress need a box spring or special base?

Skip the box spring entirely; a springy one is the wrong base for foam. At a slim 10 inches this all-foam medium is the shortest in the line, so the platform under it matters: use a solid platform, a foundation, or slats no more than about 7.6 cm apart. Foam bridging wider gaps sags and voids coverage. On a low platform bed, the 10-inch height also keeps the mattress easy to get into.