I spent the last 2 Xmas living at 180m outside Inverness and got no snow around about Xmas at all. There was a lot more snow than what everyone else living down below 100m experienced though to the point people thought you were telling lies.
My advice would be try find somewhere that is above 150m and that greatly increases your chance of a white Xmas but I seriously would not raise your expectations of getting one. You are far more likely to get a grey/wet day and even far more likely to get a full day of sunshine than a movie-like white Xmas.
Cairngorms area is good but if you are not interested in snowboarding or skiing I would avoid Aviemore like the plague. Prices are jacked up and the place is stupid busy.
If you want to be close enough to some sort of civilisation, the following places are lovely but you'll still have a Coop nearby at least:
Grantown on Spey
Tomintoul
Newtonmore/Kingussie
Ballater
Braemar
Aboyne
Up Inverness way:
Strathpeffer
Drumnadrochit (sea level)
Fort Augustus (sea level)
In the sticks West Coast (all low lying):
Torridon
Gairloch
Mallaig
Ullapool
Isle of Skye (Portree, Uig)