Just a note but I have never seen anyone living on a motor yacht full time. I can only suspect there is some issue with living on them, or that people that own them already own homes.
Your best bet would be a sailboat for living and still being able to take it out. A 30+ ft sailboat would have anything you needed living wise. A 40+ would be best for lady hunting as they are much nicer, and have at least 2 bedrooms. A mono-haul will be the cheapest option, a cat would be nicer but reflect that cost also.
Also docking fees per month can run anywhere from 500-1k a month, for electric, water, and sewer. Your basically a floating RV at that point. Dock charge per foot in length so that's why the price is so high. Its also by if you take up one slip or two.
If you go really cheap and live out in the water, rent is free. But you have to take care of the rest. water, electric etc. You will also have to get a nice dingy and will probably have to join a dinghy dock service that lets you park you dinghy when needed.