If was doing yoga in the privacy of my own home, I'd just wear shorts with a bit of spandex in them if you won't otherwise be too cold. Otherwise, just look for a workout pant or capri that is comfy and doesn't otherwise impede your movement in any way. It doesn't have to be yoga specific and there are lots of options out there that don't cost an arm and a leg.
As it is, I don't do yoga in the privacy of my own home. I wear some Nike Dri-Fit pants that I've had forever and that have really held up. They're semi-fitted through the thigh but a bit wider from the calf down. When it comes to tree pose, I have to hike the pant up to my thight because the fabric is otherwise too slippery for my foot to hold. I'd just wear shorts to my class, but I'm not a huge fan of my legs, and they're not something I want to stare out/obsess about while in poses like downward facing dog.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher