Hello and welcome to the forum. Craigslist is a great idea and I've always seen people be very open about what they are looking for in a roommate. They specify gender preference, smoker/non-smoker, drinker/non-drinker, holder of a day job vs. night job. I wouldn't hesitate to post an ad being very specific about what you want in a roommate. Don't just stop at the sobriety either, list whatever other preferences you have. Living with a stranger can be stressful enough, best to go in to it as much on the same page as possible.