1 Mattress Helper unit is needed for EACH Sleeper for maximum comfort, support and a LEVEL BED SURFACE…….. SIZING RECOMMENDATIONS:….2 of the 20″ x 50″ for a FULL/QUEEN;….2 of the 31″ x 50″ for a KING;….1 of the 31″ x 50″ for a TWIN….. EXCEPTION: If there is 1 Sleeper on a Full/Queen – they can use 1 …