I had an ugly ergonomic chairpad in my office that had seen much better days.

When I got a new desk for my office, I figured it was time to spruce up the chair, too. So I decided to sew a cover for the seat and the back.
First, I traced the outline of the top/bottom and edges of the chairpad onto the reverse side of wrapping paper, adding a quarter-inch seam allowance all around.

I decided to use the patterned fabric from the window shades I had sewn for the office, but there wasn’t enough to cover both the chairpad and the back. So I used the patterned fabric as a central band on the top and bottom, and a complementary solid red from my scrap bins for the rest. (The red is from the same fabric I used to make my living room window quilt.)
This is what it looked like sewed together, with a button added. My Pfaff has an automatic buttonhole mode and foot that made the buttonhole easy.
Here’s what it looks like buttoned:
I’ve made chair back covers for this type of chair before, so I didn’t make a pattern. I just used an older cover as a guide. This is what the chair looks like now:
Here’s the underside of the chairpad:
Lilo likes to sit on this but, miraculously, she has not tried to eat the fabric. It probably helps that I shut the chairpad in the closet when I’ll be out of the room for a while.