What foundation does this thin foam mattress need, and will it slide?

It needs a flat, firm, fully supportive surface, not a flexing box spring. A platform, slats under 3 inches apart, a bunkie board, or an adjustable base all work. Because this 6-inch foam bed is lightweight, one owner found it slid on an open metal frame; a solid platform or a non-slip mattress pad underneath fixes that. A continuous, even base also keeps the firm core supporting your spine the way it is designed to.