A patient support surface or mattress has a coverlet defining an interior region and a core situated in the interior region. An interface pressure sensing sheet assembly is provided in the interior region. Above the core and beneath the coverlet, the sheet assembly has a lattice of longitudinally extending straps and laterally extending straps that are made of an interface pressure sensing material. The lattice has gaps through which the coverlet presses agaisnt the core. The laterally extending straps are provided over relatively high pressure zones of the core, such as a heel, sacral and/or occiput zone, and are not provided over other zones of the core.
