Do you have a pair of lycra tights without a chamois? Those can be a little iffy for Tree pose and anything else where you need to brace weight against the side of your leg, but other than that, they're fine.

My very favorite yoga pants are a loose pajama-type capri with a drawstring. They're Underarmour, but discontinued long ago, I found them on closeout four or five years ago. Wish I'd bought a second pair. But if you see anything similar in the stores, I'd jump on that.