I used 97% Cotton, 3% Spandex Baby Corduroy (fine wale corduroy) from JoAnn's. It has a nice amount of stretch, but is easy to work with (except for the topstitching which I will talk about below). I also used these dungarees buttons from JoAnns that you just snap on - no sewing.
Word to the wise: DO NOT use baby corduroy if this is your first time topstitching! Or maybe even your second or third. I tried to topstitch in white - that's the look I really wanted and there was absolutely NO way to do it. As you sew you roll over each corduroy at a diagonal (if it's cut perfectly on the grainline). So, if you're trying to sew a needle width away from the edge (as Janet teaches) you will keep rolling over the cords and off the edge. I tried it for hours and had to rip it all out. Uggh. I love the baby cords, but even with same color topstitching it was very difficult to keep the stitching line where it needs to be.
Also, I accidentally used interfacing on both collar pieces - oops - the collar is stiffer than I would want - it will work find, but next time I'll just interface the outer piece. I used the Pellon medium weight fusible interfacing from Joann's. It is nice with the baby corduroy.
So, I am a size 10/12 and I made the size XS jacket with no modifications. Once I got to the end I realized the sleeves were too short and I inserted this bit of fabric between the sleeve and the cuff (to do so I had to sew the vents closed - so, no vents, but I don't miss them. I needed the sleeve to be 24" from my shoulder to just past my wrist.
Now, Janet does have one trick called the Burrito. It's meant to do something fabulous to finish the cuff, but even after watching it 3 times and trying to do it I absolutely couldn't figure it out. So, I made the cuff work, but only by my own wits :)
Anyway, this was my 4th Craftsy class and I'm totally in love. Everything I've learned in these classes is helping me in every facet of my sewing, mending, design, etc. Love Janet Pray! Her tips are amazing and she's also fun to watch. She has a nice, commanding voice, she shows each technique up close and she really knows how to make things turn out great.