I've spotted a Jason Wu black dress that might work for me. According to the size guide measurements, it runs very small. I compared the size guides for a Wu dress and a Kay Unger dress in the same size 10, and the Unger is 3" roomier in waist and hips. I've bought several of her dresses and they fit me just fine, assuming I am a very careful eater for several weeks before I want to wear it. Also, even a size 8 Under dress is much bigger than his. Bust is approximately the same.
I don't see much point in ordering something that I won't be able to zip up, or even pull over my hips. Anyway, it has a high round neck and is sleeveless--not ideal.
Why oh why do designers do this? The largest size available is a 10.