I like Le Mystere thongs (they make other styles) and the good old Hanky Panky, one size fits all thongs and hipsters. I know we've had discussions about thongs before, but you might want to check out these brands. Usually, you have to go to a lingerie store to buy them. I have found that underwear, like bike things, tend to fit better and last longer when they are professionally recommended and fit.
2015 Trek Silque SSL
Specialized Oura
2011 Guru Praemio
Specialized Oura
2017 Specialized Ariel Sport