A bolster structure system possesses anti-decubitus ulcer characteristics, and may cooperate with a mattress overlay also having anti-decubitus ulcer capabilities as part of a mattress overlay system, in which multiple elongate, positionally adjustable, relatively moveable bolsters are configured for selective placement in conditions of lateral under-engagement with the sides of an overlay to create inclined, lateral side elevations of these sides at locations along the length of the overlay. The bolster structure and overlay may each include a dynamic-response core expanse formed of an open-cell, compressible viscoelastic foam coated with an elastomeric, moisture- and gas-flow-managing, differential-thickness coating structure load-transmissively bonded to the entirety of the outside of said core expanse to function as a dynamically-responsive unit therewith.