I don't know if you'll have to go custom or not, but I don't think it's as bad as you seem to feel.
The fit in the picture seems okay as if the dress was made with a dropped waist, but a longer skirt might balance the dress a bit better. Many times you can order a dress but specify a longer skirt without much of an extra charge.
The other option would be to go with a separate leotard and skirt. That way you could get a leotard to fit, and the skirts are available in a wide variety of sizes as well.
I need to make my own dresses because I'm built funny. Imagine a 5'6" woman from the hips up, with the legs of a 5' woman. And because I lift weights I have a tank like quality. Plus 50 extra pounds. Sigh. None of us are perfect.