You should carefully adjust your saddle height and the way you sit on it. Stand the hipbone and don't slide (or rub, whatever) your hip on the saddle, just be stable. Proper siting position is crucially important. For me 200lbs, I can go more than a hundred miles without no shorts or bibs.(Though it hurts a lil bit afterward.) If you don't sit properly, any shorts or bib can't help you. It's just cheating.
If you're light like 130-150lbs...then Pearl Izumi Quest would be enough. For more comfort, I'd recommend Assos or Etxeondo, but kinda expensive.