I bought a $2 Faded Glory Onesie from Wal-mart and had the fabric from Nan. I didn't want to spend too much on the onesie in case this turned out to be a ginormous mess. I tweaked some of the details, but for the most part followed the tutorial exactly. If you are new to sewing clothing you might be interested to know that (for me) the most challenging part was sewing the skirt onto the onesie. The tutorial says it doesn't matter that her stitching isn't perfect, but I can say from experience--it does. I had to do two stitchings because the first time I did it the skirt didn't attach in all areas. I was bummed.
After attempting to remove the seam, I was worried I'd tear the onesie fabric. So I decided to just re-sew the skirt on, this time further away from the edge. I'm sure this pattern is much more forgiving than others, it's just not forgiving enough for this beginning seamstress. LOL
Another change I made was due to another mistake I made. LOL (it's a learning experience, right?) Since sewing the skirt part on twice, it made the dress look bulky where the fabric folded underneath the onesie (you can kind of see this in the pictures of Natalie wearing the dress), so I decided to cut it off. Well, in doing so, I put a nick in the onesie. :( After careful thought I chose to make a fabric flower using a basting stitch and bunching the fabric. Then I attached it over the nick and all is good. :) I actually like it a bit better because it adds dimension to the dress.
Overall, this is definitely a dress I want to try again. Nat seems to like it, and I'm sure it'll get easier to make the more I try it. Plus it's so adorable!