I bought the materials at Walmart, including the onesies. Just as an FYI, I checked out both the Gerber onesies and the Baby of Mine (Walmart brand) and liked the thickness of the Baby of Mine much more, so bought a pack of 3.
I ended up making them all the same. I thought they turned out pretty good for my first attempt. Especially, since I pull out my sewing machine about once a year to use. I may just have to make a few more. I plan to give these away as gifts.