Pre-op I liked underwear with a wide gusset and thin elastic around the leg holes. That way it created a "pocket" for my lips, with firm borders that would stay in place and not let a lip slip out when I moved and leaned. My go-to was Maidenform cotton bikinis - You can see on the very thin model that the crotch is wide, lol. (IMO don't buy from Amazon, their prices are high; I found them a lot at places like Kohls, JC Penneys, Ross)