You’ll need two 17 inch square pieces of fabric and a 20 inch zipper. You’ll also need a zipper foot for your sewing machine (which probably came with your machine.)
Leaving the zipper closed, place it on the end of the fabric you want on the bottom of the pillow, right sides together (meaning the zipper pull should go towards the printed side of the fabric.) Using your zipper foot so you can get as close to the teeth of the zipper as possible, sew it to the fabric, keeping the edge of the zipper aligned with the edge of the fabric.
Open the zipper up all the way, then align your fabric to the first piece, right sides together, so that the zipper will be even on both sides. Put a straight pin in to hold it in place, then repeat the steps to attach it to the second side. Yay! The hard part is over!
Now zip it half way – do not zip it closed – then line up the fabrics and using the regular foot on your machine, sew around the other three sides of the square with a 1/2 seam allowance. You are going to start by sewing right over the zipper, back stitching to lock it in place.
Snip a little off the corners to make it easier to turn out – then turn it out and iron it.
Add in an insert and you’re good to go! Big change, little time, small budget – gotta love that!