Hi! I'm not a yoga expert, but started doing yoga this year at a community center that advertised "Yoga for Absolute Beginners." It's been pretty great. The teacher is very affirming, and there are all sizes and shapes in the class. She gives modifications at every step. If you can go to a beginners class I would recommend it (I would call ahead and confirm that the class is *really* for beginners, because I got burned at a class at a different location that was actually fairly advanced).
For YouTube, I hear good things about the "Yoga by Adriene" channel. She has a lot of videos, and keep meaning to try them, but just haven't yet.
Good luck! I hope you like it! My one class a week has been a really good challenge, as someone who is also not very flexible and with terrible balance!
Yoga?
