Oh okay. Sarah (sarbear1121) has this dress in black. She quite likes it, and it's very flattering on her. She is an hourglass than tends toward a pretty pear. I have other J. Crew dresses in that cotton sateen fabric, and it's not wrinkle free (like if you're sitting for a long time, you might get "lap" creases), but it's not any more wrinkly than an other cotton sateen fabric. Does that make sense?
I've tried it on, and in my experience, it runs true to size (for J. Crew). So whatever size you normally take in J. Crew, I'd go with that. If you are between sizes, go with the larger size.
