I don't know what to call it ... Shift? Chemise? Shirt? Shirt is probably closest, as it's rather ... abbreviated.
The fabric we found in the slightly greenish color we wanted (it very quietly sets off the dark orange very nicely) was in rather short supply. There was maybe a yard and a quarter or so, but we grabbed it, and I figured I could always piece some muslin or something onto the bottom where it wouldn't show.
I scaled down the pattern I'd used for my camicia (Italian shift) and realized we were still short fabric. So instead of folding the fabric length-wise, I folded it width-wise. This is a pattern with raglan sleeves (the sleeves and shift front where the sleeves attach are cut at an angle, instead of more fitted, set-in sleeves) and I planned to use the finished selvedge edge of the fabric around the neckline opening.
After washing and drying, I had about 42" of width (turned sideways, so now it was length) to work with. I cut the body 30" long, and the sleeves 12" long, figuring they'd be hidden under the velvet sleeves anyway. I carefully folded the sleeve portion over twice, so I could cut both sleeves at once and guess what? Bad news: I cut from the wrong folded edge. Good news: I stopped when I realized what I was doing.
I had to flip the sleeve around so the mis-cut armhole was now on the hem edge, and I could cut the armhole correctly. That part about the finished edge forming the neckline was right out the window and I didn't have any matching thread, so I improvised. The undergarment in the movie has a very subtle X pattern embroidered around the edge, IIRC. Instead, I turned the edge over and used an embroidery stitch over the raw edge in a slightly darker shade of green.
The outside edge is visible on the left, the inside portion is the vertical part on the right. The ivory-colored tape is the casing for the ... elastic. Yes, ELASTIC. Not a drawstring. Get over it.
The next step, was to fix the armhole cuts in the sleeves. I simply took wedges out, removed some of the fullness and called it a day.
The finished garment is long enough to come down to mid-thigh, and the sleeves won't show under the finished bodice.
It's a little more full around the neck than I'd like -- I should have cut it on an A-line, but lesson learned. The only bit that's going to show is the ruffle around the neckline of the bodice, anyway. It's just a costume, remember?