I like the idea of committing to a specific period.
Honestly, just saying "I'm not drinking anymore!" sounds bit hollow after having said precisely that at least half a dozen times before. "Never again," says the drunkard the next morning, to the disbelief of all in earshot.
"I'm not drinking at all for a year" seems like it will make it a bit more concrete and less daunting. Three months was doable, next up, 12.