Hey! I'm a female to male transgender runner! I understand your worries, but honestly you'll probably be fine. Unless your upper thighs together a lot (no thigh gap) then the extra fabric doesn't make any difference. I would suggest boxer briefs, or undies like those, to any runner regardless of gender because, in my experience from running in female and male clothes, mens clothing is all around better for running. Hope this helped!
Thank you! A little more confident about dropping them $$$ now =)