My DW & I just finished "Operation King bed modification"! Woot!!
Just Installed the new "Mattress Insider" 5.5" Sedona mattress. It feels like it will be great for us.
I started by removing both shelves/cubby holes from each side of the bed. Swapped my narrower one to my wife's side. Had to cut down her top to fit correctly. Then, used 1/2" sanded plywood to make an insert to fill the backside walk around. I used the same plywood to make two hinged V- boards to support the insert. It is completely removable when needed. I will install a small corner shelf for a clock to Velcro too on my side.