Petticoat / slip over your shapers?

You should really only need a petticoat if you need to add more fullness or shape to your dress. Since it's a sheath gown, that's unlikely. If the fabric is clingy a slip could help it from going between your legs when you walk. Amazon has inexpensive options that you could try on with your dress and return if you don't find them necessary.

Hey there, April! I agree with Caytlyn! You could always buy one to try and return if you don't feel you need it