When I created my workbench a few years ago, I designed it to function as both a standing desk and a normal desk. This is quite convenient because if I need to move around a lot, I don't need to get up and sit down a bunch, but if I'm doing something that takes a while, I can still sit down. The only drawback is that it's too tall for a regular chair and thus requires a taller stool, which is unfortunately not the most comfortable, especially if it's a old wooden one like mine. Although I would love to have a backrest on the stool, that's a little impractical for a workshop stool that doesn't swivel around. The next best thing is to make a nice soft cushion.
Step 1: Cut Out the Materials
First I cut out a circle of 2" rubber foam slightly larger in diameter than the top of the stool. Then a circle of fabric, I used fleece, but it's not terribly durable, the circle should have a border about 3" past the foam. Neither of these circles have to be perfectly circular or of precise size, you can see my foam circle is actually made of two pieces.
Step 2: Create the Drawstring
Here, take some pins, or, like me, alligator clips, and fold a lip in the fabric circle. Stitch the edge of the lip, make sure to leave room in the lip for the string to go through. Next, tie an electrical lug onto a length of paracord or string and cut it, making sure to leave plenty of length for the string to go around the diameter of the stool with some extra. Use a lighter to melt and fuse the cut end of the paracord. Feed the cut end through the lip in the edge of the fabric and through the screw part of the electrical lug. Place the fabric over the foam circle, pull the string, and it should partially encase the foam.
Step 3: Put the Cushion on the Stool
Loosen the string, place the cushion on the stool, pull on the string, and tighten the lug screw. There it is, a nice comfy, cushioned workshop stool. At the time of writing this, this stool has actually been in use for about two years now and it's still holding up great.