What I've found has helped the most is moving into a house with a real office in it and only working in there.

My condo was a work free-for-all. Working variously in the kitchen, bedroom and living room imbued the entire place with an emotional vibe that made it feel like I was always at work, even on weekends.

Also: Laying down the law and getting family to respect that you are at work when those office doors close. No requests for chores, no constant pop-ins for idle chit chat or (much worse) picking fights.

I've found these things work whether I'm in my underwear or not.