I am sorry to hear about your Mum. I don't care what age someone is but to lose your Mum is a sore thing.
Christmas in Scotland is an odd time. It's for some heaven knows why reason, a touristy time, and that makes it expensive for hotels, B&B's. But, the caveat is that much of the tourist provision is shut for the season so there's nothing open, not even pubs in many rural areas.
Bothies, which are free, are generally full on though because the natives are on holiday and many of them take to the hills. So, those are inclined to be crowded over Christmas and New Year, especially if there's dry weather or snow.
There's also the point that there is (if you're lucky) eight hours of daylight at that time of year. It's a long time to sit in the dark, if I make myself clear.
I feel as though I'm being terribly off-putting, and that's not intentional.
I think best advice would be to look at places such as Comriecroft (in Perthshire) or Red Squirrel campsite in Glencoe. Both are accessible, both are sites folks on the forum know and like, and the staff at both sites are both helpful and welcoming.
I'd say the islands, but you can't guarantee the weather, especially in Winter, and that means you can't guarantee the ferries, so I'd say stick to the mainland or Skye (bridge across). Depends on how much time you have, the ferries will run, eventually.
If you want to go further north, maybe speak to Ian Deveney,
https://www.invernesscustomtours.com/ian-deveney
Ian's sound, and has a wealth of information and connections right across Scotland.
