We settled on this dress by the Japanese company Mary Magdalene.

Front

Back
The basic shape of the dress was easy to pattern, but the sleeves proved to be quite a challenge. They are essentially raglan sleeves that are elasticized at the shoulder and hem. I drafted them as actual sleeves with an underarm seam, and this made it more difficult than if I had just made them like really wide straps with no underarm seam.
Another interesting part was the center back panel. I put a seam at the waist of this panel, and the top section is a double thickness, with channels stitched across to accommodate the elastic. The elastic pieces were cut to a specific size and tacked at either end.
Everything else was pretty straightforward, just lots of lace and trim. There is a small invisible zipper at the waist on the left side seam. The dress is made of 100% cotton sateen. It is not lined, due to time constraints on construction.