So when I started my consultancies back in the day it'd be me or me and 1-2 other people for a long time till we built things up. What I'd usually do with clients is send them written communication that I planned to be taking time during whatever period and would be either totally unavailable or available on emergency basis (which I would charge a larger hourly rate for). I'd always try to communicate this 4-6 weeks in advance where I could and then remind them at regular intervals via email so know one could say I didn't communicate. Also, make sure as you are scheduling work that is factored into the schedule and then it is all good.

Also, I am US based but I never had any client complain or bitch about it. And only a few clients from time to time would call me for emergency support and not a single one complained about having to pay a much higher rate because it was a legit issue. I did have a couple of clients try to contact me when I said I was completely unavailable but that is just life.

I also setup auto reply emails with specifics to be clear, and how to reach me in an emergency. As well when we were growing and had more people available we'd cover each other's projects so there was literally no interruption.

The key is just communication early and often. And set clear boundaries on your time, not just your holiday time but your daily time. Do this and you will rarely have issues, except for those few asshole clients we all seem to have from time to time.