We have a king sized bed in our 5th wheel which is basically pretty comfy. The problem is it uses a woven strap lattice, supported by a thin wall 1 1/2" framework so the KS bed tends to sag a little i...
We had a similar problem in an old class a we owned, 3/4" plywood solved the problem! If you have storage under it, you can reuse the piano hinge from the 1/2" you are replacing, DIY plan on at least 1/2 days work to remove and replace the plywood. Depending on your floor plan you may have some tight conners to navigate getting the plywood into place, and probably require assistance.