A mattress cover for a mattress providing movement therapy to a patient. A patient support portion covers the upper surface of the mattress, and a bottom portion is coupled to the patient support portion. The mattress cover may substantially encase the mattress. An augmenting feature is associated with a peripheral portion with the augmenting feature adapted to move between a stored configuration, and a deployed configuration in response to increasing thickness of the mattress during the movement therapy. The augmenting feature may include concertinaed material, such as thermoformed plastic, and/or a fold of material coupled to the peripheral portion. The patient support portion and the bottom portion may at least partially overlap and be moveable relative to one another. The mattress cover may be included on a mattress overlay having a patient turning device, or on the mattress supported on a patient support apparatus.