Ask the CL owner of the regency headboard if they could measure the width at the widest part of the headboard, which is where the headboard curves out on each side just below the top line. I am betting that it will give you a couple of inches of width on each side which will balance the difference between the 54" width of the full mattress and the 60" of the queen. You will also be able to disguise the difference a bit by how you place the pillow shams on the head of the bed.

Recently, my friend and I made upholstered headboards for our daughters. They are queen sized, but no reason you couldn't do full. She made hers from hone-dec fabric. I used an old mattelasse bedspread. If you are interested, email and I will send you the directions I wrote up.

Not sure why you want to keep such a heavy, dated piece of furniture when you have a great opportunity to improve and upgrade the style of your bedroom. I would sell that on Craig's List or FB Marketplace and use the money to apply on a new headboard that actually fits your mattress.

Vote yes for toe testers! Note: They are not tripping hazards. Unless you are someone who likes to lean on shower walls. The wall that has the shower controls. 😊 Our original one was put in when the house was built in 1968. Its now a guest room bath, but was used numerous times daily when it was our children’s bathroom. Never a leaking or cleaning problem The one we had installed when we ripped out the jacuzzi tub in our en suite to make a big walk in shower is used daily by 2 people for over 10 years. No leaking or cleaning problem. There is no need to balance to use it properly. You just stand close enough to the wall with the controls so your toe gets hit with water. Then you back up.