A quote from Sylvia Boorstein that I find helpful
The Truth of the Breath
Some people practice throughout their entire lives just by paying attention to their breathing. Everything that is true about anything is true about breath: it’s impermanent; it arises and it passes away. Yet if you didn’t breathe, you would become uncomfortable; so then you would take in a big inhalation and feel comfortable again. But if you hold onto the breath, it’s no longer comfortable, so you have to breathe out again.
From Body as Body