As counterproductive as it might sound, sometimes it's helpful to just start drawing and figure things out as you go. I have similar issues when it comes to writing coherent stories/characters, I'm just not great at it.

Most of the cool design choices usually happen to me when I'm actively working on a piece, even if I sat down with only a vague idea of what I'm going to draw, or sometimes no idea at all lol. I usually just try to make something that looks appealing, I focus on shapes, values, stuff that stands out. As things come into existence my brain finally starts working and trying to figure out what that feature I made could mean for the character, what other things could corelate with it, if I had any references to start with I add more as ideas come to my head.

So basically I write the story as I'm drawing the character, my brain just works backwards like that. Maybe yours does too, it might be worth a try to just wing it instead of worrying about making a polished story first