You sound like you're pretty handy with woodworking tools. How about a box that sits on the floor and attaches to the head/foot boards using the locking cleats. The only function the head/foot boards would have is appearance, the weight would be carried by the floor. The box would give you a lowered set of side rails. The attachments (the end of the box)might have to be extended vertically to attach on both ends, and possibly have legs at the attaching points. Depending on the configuration of the foot board this may or may not work. Just an idea...Hope it makes sense...

Wayne, I do appreciate all your posts. The existing cleat slots in the headboard are about 51" apart. To avoid conflict with the mattress set, the mattress etux would have to be offset toward the footboard to clear the cleats and whatever they are mounted on. Not ready to do it that way. For my Mother-in-law who had an old single bed that was too short but almost the correct width of 39", I just drilled a couple of holes in each headboard leg, installed tee-nuts from the back and used machine screws (stove bolts) to attach a steel bed frame, no footboard used (it is stored). There is one "rope" bed also. Ropes under tension were used to support a "tick" which was a huge bed-size "pillow" used on the bed. Filled with dried leaves or straw for the children, feathers for the parents. Children got fresh leaves or straw once a year. Sleepers sank deeply into the tick and quilts on top made sleeping in winter without heat tolerable. I did sleep on a (straw) tick while visiting relatives a few times in the 1940's. Anyone ever seen one of these used with conventional mattress?

You sound like you're pretty handy with woodworking tools. How about a box that sits on the floor and attaches to the head/foot boards using the locking cleats. The only function the head/foot boards would have is appearance, the weight would be carried by the floor. The box would give you a lowered set of side rails. The attachments (the end of the box)might have to be extended vertically to attach on both ends, and possibly have legs at the attaching points. Depending on the configuration of the foot board this may or may not work. Just an idea...Hope it makes sense...

Sorry about the double post. I had left the computer and forgot I had already submitted it. Such comes with age I guess....

My earlier post had some error in terminology. The part I called cleat is really a bed rail hook, similar to Rockler #38606. I do have a vertical milling machine and 3 types of welders, so perhaps making offset bed rail hooks is a possibility. But using such changes the forces placed on the pins in the headboard legs from simple shear to a combination of torque in two directions plus shear. Gotta think that one through. One other possibility is to make the longer rails as needed for double bed mattress, hook them in the existing slot and pins, make 3/4" plywood platform to rest on the top of the rails with nominal 1 1/2" cantilever overhang on each side and just use mattress on top of that to keep height about right, no "foundation" used. Anyone ever seen offset bed rail hooks for sale? I still need your creative ideas.

We have a rope bed! I had a matress made to fit at a factory that was willing to modify as long as the configuration of the springs did not change. I think we used one row less in the width. We still use the ropes and our guests often comment on how comfortable the bed is.

Buy or make the hooks and weld the arrangement together and attach to the new, longer rails which will be lowered by the process.. You're right on the added stress but I think it wouldn't be enough to endanger the HB/FB. If you make an offset bedrail hook you can weld a flat shoulder plate at the junction of the plate and HB/FB to minimize any movement. I'd just buy the hooks and then make the steel offset to the size I needed it. Both sides can be connected together to add strength and possibly with hidden legs to hold the weight and minimize the racking of the bed. This is the idea I referred to in my first post. The "no foundation" idea makes sense, and may well be the best solution, that surely would be the easiest, but you'll lose the padding afforded by the foundation and may lower the top of the matress below "where it should be".

I recently learned that rail systems are made to convert "full" size beds to accept "queen" mattresses. Found it with Google Search. Priced about $75.00. This could be (gasp) copied for my application or purchased and modified.

Bus Driver, There is a Mattress manufacturer in Nashville, Tn. that will make you a box springs and matress for any size bed. I can't think of the name right away but if interested mail me direct and I will get the manufacturers name.