When it came time to select a pattern for my costume, I needed something that was tightly fitted to either the waist or the hips, with a sweetheart neckline. Traditionally, Wonder Woman's belt is at her waist, but since my costume will be extending much further (since I will be swapping out panties for a skirt), I don't want to OD on blue with white stars. Fitted to the hips sounds better to me.
I have been unable to find a dress that fits those criteria, so I have decided to adapt a corset pattern. Butterick 5797 (view D) is my choice, and it shouldn't be too difficult to add a skirt to it. I don't have a skirt pattern picked out, but it shouldn't be too hard to steal one from a another pattern or draft one myself.