Hello Christine! Can you add a picture of your old cot so we can see what you have to work with! I am certain someone can come up with a way to turn your old cot into a double bed headboard!
The only thing I could think of was to fold it flat and mount to the wall. This would be of course after cleaning thoroughly. Then center the bed under the cot.
I'm having a hard time picturing it. Is a cot as in a crib, or a folding canvas cot?
Depending on what type of cot it is, you could probably just hang it right on the wall.