Slips and bodysuits are both great options for anything form-fitting (think: mermaid or slip dresses) as a continuous undergarment will help to avoid any visible lines and creases. Ideally, minimal shapewear works well with more loosely fitted attire (think: A-line dresses and ball gowns). Finally, consider any other details that might dictate what kind of shapewear you choose, like if your dress is backless or has a high leg slit.
Another thing to look for in your wedding underwear is comfort. It's a good idea to test it out before the big day to make sure it's breathable and doesn't roll up or down. And most importantly, keep in mind that you'll likely be wearing it all day long—don't let an uncomfortable undergarment take away from your wedding experience. The good news is that there are lots of comfortable and high-quality options out there to choose from.