Full size bed and mattress combo is a single individual frame measuring smaller in diameter than a full bed frame can sleep two people. A standard full size mattress measures 54-inches wide and 75 inches long. You can use your three-quarter mattress frame and convert it to a frame that can include a spring mattress and full size bed and mattress combo with a few basic supplies bought from your home improvement retailers.
Cut a piece of 1-inch thick furniture-grade plywood to the dimensions. However, the first measure your actual mattress with a tape measure for a precise fit. The plywood will serve as a pedestal top. Place the plywood face down on the floor and place the top of the bed frame on the plywood. Center in the bed frame from top to bottom and left to right. This will distribute the weight of the mattress of the frame.
Four evenly spaced holes the length of each rail of the bed frame. Drill holes but the bed frame and through the plywood. Line up the mounting holes. Thread a 1/4-inch nut on the end of each bolt and tighten the nuts and bolts with a wrench. Place the full size bed and mattress combo on plywood sheets.