I have four to choose from.
I also have an additional long white knit tunic that could be substituted for any of the tunics in these to be more modest (or line the one piece version to make it more opaque.)
Long White Polyester Tunic.
Has a waist built in, Meant to be worn under Ghost Cape, Can also be used as a tunic under a toga.
Or as a base for an Angle.