A therapeutic mattress assembly comprising a mattress having a substrate assembly that includes a plurality of cylinders positioned side by side over the length of the mattress. Each cylinder is configured as a low air loss system to allow air to flow into the cylinder from a source and out of the cylinder through small holes located on the top of each cylinder. An overlay assembly provides a foam cushion that provides a supporting surface above the substrate assembly for the patient. A calf lift bladder operates to effectively raise or lower the patient's feet to prevent pressure related injuries. A lateral rotation assembly selectively raises and lowers a selected half of the mattress to turn patients in a lateral direction. A bolster inflates in response to the lateral rotation assembly to secure the patient within the mattress.