I don't see any support in the suttas for this approach. IMO it is better to stay with the breath than add words and mental clutter.
Alternatively, just chant a mantra, which is a practice with different assumptions and goals.
You can try Vajra recitation
Om - breathe in
Ah - hold
Hum - breathe out
Alternatively, So Ham is another commonly used phrase. Its the sound of breathing in and out spelt out phonetically. More yogic than buddhist though