If you want breathing exercises that go way into the specialized deep end, you can always pick up the sport of 3p rifle. You'll get incidentally very good at calming via breath, because of the tight feedback loop of holes-must-go-closer-to-the-center

See e.g. Reinkenmeier describing breath work in

standing: https://youtu.be/dHsG3GU9_PY?si=qlaLrSfKLCeiCgl4

prone: https://youtu.be/5odRbYSbDIk?si=joBeFyyUrwBvQ7bk

Just general: https://youtu.be/JJ3zXuFsrfk?si=xdQ5NY0cHfK89CCg

The general points (deep from diaphragm, lean back, relax shoulders, etc) also carry over to other discipline like music (wind instruments at least).