Looking for pattern for pillow back with button closer

I made a large square with a tiny sweater on it that I was going to put in a afghan. But my mom fell in love with the square so I thought I would turn it into a pillow for a Christmas gift. I’m having trouble finding a free pattern for a pillow back so that my mom can take the cover off for washing.

Any help would be greatly appreciated.

Maybe these will help.


Thank you Jan