If you want to learn more about breathing I recommend checking out the book The Oxygen Advantage by Patrick Mckeown. It's got a bunch of different breathing exercises and ways to measure progress. It basically reteaches you how to breath too, which is fascinating on its own. Worth checking out for sure. https://www.amazon.com/Oxygen-Advantage-Scientifically-Breat...
Breath work and cold exposure have been a large part of my life after reading 'What Doesn't Kill Us' by Scott Carney [1]. That was the book that drove me want to experience it first hand.
[0] https://www.goodreads.com/en/book/show/48890486-breath [1] https://www.goodreads.com/book/show/30039048-what-doesn-t-ki...