What's a femme to do?

Now, I have a fairly vast wardrobe. I have dresses and skirts galore. A plethora of high heels and stockings with backseams. And I have a large wardrobe of slacks and sweaters and other sensible, moderately respectable clothes for teaching. But there are some occasions for which none of these things are proper attire. Sadly, I'm tragically unhip and don't do casual wear well. So I often show up to plays and events somewhat overdressed, but I usually shrug this off as femme performativity and all in good fun.

Today, however, like many other days, I find myself in a casual daytime situation for which I have absolutely no solution. I want to be more hip and less formal than my sweaters for teaching and I want to be comfortable. But I have not mastered the art of cute t-shirts and jeans or any other appropriate look for the days when a retro halter sundress isn't quite right. How to be cute and femme in jeans? What can I wear that's resistant and slightly punk without overdoing it? My gay best friend tells me that I have not yet mastered the art of the little black t-shirt, which can solve so many of these problems. He's right; I own far too few t-shirts. There are the old ones that I sleep in, and a couple I've picked up at concerts and shows, but I own very few t-shirts that are actually anything resembling cool. I've only begun to accept the idea that I can pull off a tight-ish, girly t-shirt rather than a huge baggy men's t-shirt, which is never particularly cool. I only buy a t-shirt if I really, really love it. It has to both look cute and say or support something I agree with. I own very few slogan t-shirts because there's a very high threshold for accpetability. I'm fine with t-shirts with just pictures on them, though, as long as the pictures are cute and I can explain where the t-shirt came from if asked. So I'm asking for help and taking suggestions. What can and should I wear in casual situations? What cute t-shirts should I own? Help!