Last night I did some more experimenting and started on a 20s step-in, like this one here.
http://www.knowlesville.com/vintage/1920-teddy1.html It's essentially a short slip with a little flap that buttons underneath the crotch. I made it from some cotton voile, and I want to add lots of white lace and pink ribbon. At some point I would love to make one in some silk crepe or rayon, but for now cotton voile is what I have.
I'll post some pics when I'm done, but I'm afraid you're not going to get to see it one me - it's VERY sheer!