That will depend on your fiance’s taste and your body type. You want something flattering that he will like. Different men have different tatse. To that not, you want something that you are comfortable in and makes you feel sexy.
The first choice will be babydoll. Your basic babydolls are always classy, either with underwear or without, paired with a matching g-string and highheels. You can get any color or fabric babydoll so there are tons of options.
Long silk or satin gowns are very elegant as well as sexy. A long satin gown in the color of you and your fiancé loves is lovely to have. If these are not do for you, you can try a bra and panty set, maybe lace set to surprise him.
Whatever you do, do it with confidence, that’s where the truly sexy side comes from!