Trade in your traditional sheets for stay cool sheets. Stay cool sheets wick moisture away from your skin and are designed with breathable fibers that allow your body heat to more easily escape from the fabric, which will reduce the heat on your memory foam mattress. For best results, try wearing breathable nightclothes as well.
Cover your memory foam mattress with a mattress pad or topper. The mattress pad or topper will keep your body from making direct contact with the memory foam, which will prevent the memory foam from absorbing your body heat.
Try adjusting your thermostat to a lower temperature, such as 65 degrees. A lower temperature will affect the heat in the air for your memory foam mattress to absorb. Plus, if your body is cooler, the memory foam will have less body heat to absorb from you as well.