Most Helpful Girl
https://www.herroom.com/Lingerie-For-Men.aspx (this looks like a really good site. it's underwear designed for women, but men are giving reviews and stating what's comfortable on men and what not. you might find something there)
if they're too expensive, then maybe just buy panties from a shop. look up a woman's sizing guide online and compare it to the men's sizing guide. figure out the best size and go buy it. they'll probably assume you're getting it for a girlfriend. and even if they realise you're crossdressing, just breeze through it. their opinions shouldn't matter, just do what makes you happy.
Most Helpful Guy
If you can find the right side get some lace from Victoria's Secret.