Remove your mattress and box spring from the bed frame. Measure the width of the frame with the tape measure.
Purchase 16 2-by-4-inch wood planks cut specifically to the length matching the width of your bed frame.
Place each of the planks across your bed frame on the ledge formerly holding your box spring. Arrange the planks so they are the same distance apart.
Lay the mattress onto the planks carefully so as to not shift the planks while placing the mattress onto the bed frame.