Although you don't mention where you'll be living or how much you've got to spend, here's what I'd suggest:
1. Identify the marinas in your area that permit live aboards. Take a look at their facilities and compare their costs. Determine if they have any space available for you. What sense does it make to even consider buying a boat if you'll have no place to dock it?
2. If you find a place, see if you can speak with any of the folks who live there. Get their feelings about the owners and facilities. See if you can get answers to your live aboard questions to see if this lifestyle is right for you.
3. When it comes to buying a boat, my advice has always been to buy the biggest boat you can afford. You can never have too much space. That 27 footer that's perfect for you, will get awful small if you have company over. For example, my 30 ft. Hunter is fine for 2 persons, but doesn't have enough room to comfortably accommodate overnight guests.
4. It's a buyer's market right now, so if you decide to go with the live aboard lifestyle, take your time looking for the "right" boat. Once you find it, have it professionally surveyed.