I'm surprised, if you're that intensely into Irish dance (I'm assuming you're performing competitively or about to be) that your coaches aren't building in stretching/flexibility for you or making recommendations in some way. Unless they like injured dancers...?
I would suggest a foam roller to make sure you're loosening everything well and some solid core/weights work to help with that straight posture/balance thing you're looking at. You mentioned something about cross-training, what are you doing currently?
As far as specific yoga stretches, you want lots of hip openers... this is a decent set here:
http://www.prevention.com/fitness/yo...open-your-hips
Good luck!