I took the other one off and used it as a template on the new fabric, allowing 1" seam allowance. The plan was to double fold it and make a channel for a drawstring.
I used an erasable pen to draw around the old fabric.
Speaking of erasable pens... I've been looking at sewing tutorial videos online and a couple of the sewists recommended Frixion pens which erase with the heat of the iron. Unfortunately, they are only available online which would cost extra for postage. Being the thrifty girl that I am, I wondered if a regular erasable gel pen would work the same. I bought a two-pack of PaperMate Replay erasable gel pens to test out my theory.