“Your underwear is showing.” Nothing is more disheartening than hearing that.
Thongs are appropriate for tight clothing {pinterest}.
Some ladies might prefer to let it all hang out and not wear any underwear but that is incredibly risky, and it can be uncomfortable.
There is a variety of underwear that women should own that would work with whatever outfit they are wearing.
Thongs and G-strings

Wear them for pencil skirts, bodycon gowns leggings or any tight cloth.G-strings make sure your outfit fits better {pinterest}
Brazilian briefs

If you are not comfortable with G-strings and thongs, you can always wear Brazilian briefs. Wear them with shorts, skirts and pant trousers.Brazilian briefs offer coverage and are less likely to show under your outfit {bizarreintimo}
Seamless pants

Incredibly comfortable and can be worn with body con gowns, pencil skirts and or any tight outfit.Seamless pants are intimate and comfortable {cosmopolitan}
Classic briefs

These are comfortable and free. Wear them on free jeans, pleated skirts, flared skirts and flared gowns.
Boy shorts

If you are a big fan of boy shorts you can wear boy shorts on flared gowns or skirts or free outfits.