Cut 90-inch long sections of batting to cover the height, edges and four inches on the back of the 3-foot tall plywood panel. Batting varies in width; you will not be overlapping the batting.
Spray adhesive on the face of the plywood panel. Press the batting strips onto the plywood. Fit the batting strips so the edges are touching.
Flip the plywood panel over so the batting side is face down. Spray the edges and a two-inch perimeter around the back side of the board. Pull the batting over the edge and staple it to the plywood with a heavy duty staple gun. Begin stapling in the center of each edge and work your way to the corner. Fold the batting at the corners and staple it to the board.
Cut a 92-inch long strip of 54-inch wide upholstery fabric. Place the fabric face down on a flat surface. Center the plywood, batting side down, onto the back side of the fabric.
Pull one side of the fabric over the plywood and staple it to the board. Work from the center to the corners. Fold the corners and staple them in place. Continue to work your way around the plywood panel, pulling the fabric over and stapling it from the center to the corners.
Locate the wall studs behind your bed. Screw the wall sections of two wall hangers into the wall, one in each stud. Screw the remaining piece of the wall hangers to the corresponding backside of the king-size headboard. Hang the headboard on the wall.