To make your own super simple, fast and easy baby changing pad all you need is a hand towel (I bought one that was 21" x 16") and cotton fabric.
First measure the seams that are already on the towel to determine how big your fabric needs to be. For example... the width of the towel is 16" and along those edges the towel seam is 1/4".
Do the math: 1/4" (seam size) times 4 plus 16" (towel width) equals 17". Then add an extra 1/4" to allow for the bulk of the towel. So your fabric width in my example for a 16" wide towel would be 17 1/4"
Do the same for the length of the seams. The end seams on towel short ends are always wider than the side seams. On mine they were half an inch. Just adjust your math for the seam. 1/2" (seam size) times 4 plus 21" (towel length) equals 23" plus 1/4" to allow for bulk equals 23 1/4".
Now smooth out your fabric and place it WRONG side up. Place the towel centered on top of it so that your fabric is overhanging.
I found the easiest way to do this was to iron, fold over and pin along the length. Then take those to your machine and top stitch. Then go back and iron, fold over and pin along the last two ends and top stitch those ends in place.
There are several options for keeping the changing pad closed. I choose to fold my towel in half lengthwise, then roll it up and stitched a length of elastic so when it's rolled I can just flip the elastic over it. You can choose to add velcro, or elastic and a button. Or choose nothing at all and fold it up and throw it in the diaper bag.