Just finished re-reading Breathing Alive - a guide to conscious living by Reshad Feild.
It's a wonderful book of teaching stories to read and absorb. In the appendix he presents a simple breathing method involving the solar plexus and the heart center.
I bought my second hand copy in my local Oxfam bookshop. Inside the front cover a previous owner handwrote a quote by Deng Ming-Dao
" You breathe
Frosting mountains white
Exciting trees to verdant flame
Dancing sparrows on your wing
Swirling waves into long sighs
And all things live"
Here's a link to the book from World of Books https://www.worldofbooks.com/en-gb/books/reshad-feild/breathing-alive/9781852300500