I have found Victoria secrets and calvin klein have sexy and comfy pairs to choose from. both you can buy online but it is best to buy a pair in person first so u can feel the material u like and usually I've found a men's large underwear will be either a ladies large or xlarge depending on the cut. so if u like thongs or G-strings, they are a little harder to wear to hold everything in. low rise is also harder to wear. I find bikini's, boyshorts and cheekys are the best. good luck finding some pairs.
The first time a guy bought me a pair of panties, he got a style he liked at a store he preferred and told me, he saw those those and just knew my ass would look great in them, so he just had to get them... so it's not about where you get them or the style they are... it's about PRESENTATION lol... make a woman feel like she'll turn you on and looks hot and she'll wear a friggin rag if you ask her to.