To balance out all the naysayers above, I lived aboard during and after the Divorce. I have to say that those were some of the best times of my life! A couple of nice restaurant and bars within walking distance, met some good people who were also live aboards, able to easily lock the door and jump on a plane to get away for a quick jaunt without a house and yard to worry about. I was lucky enough to end up with girlfriend that I met on a boating trip in the San Juans who loves boating. All in all, no complaints.
As far as the boat, Mine is 38' and I don't think I'd try anything smaller. A separate stall shower is a must. The larger boats obviously have more creature comforts, but depending on your abilities, are tougher to single hand. I liked getting out of the marina on the weekends and 38' is easy to single hand.
As was mentioned above, I'd visit the marinas that you'd like to end up in and see if there are any potential boats there. Buying a boat that you can assume the moorage can sure make things easier.