Do you mean a jersey/knit type dress? I think that would be ok for a wedding, unless it was a super formal wedding. You'd want to dress it up with heels and some big jewellery/belt/smart bag.
I'd probably look for something that isn't black or grey as colour looks a bit more dressed up/made an effort. So that means probably Jigsaw/Toast would be better than White Company. this one from Jigsaw would be a nice option, also comes in burnt orange. Big chunky necklace would look good.