I worked into it slowly and it felt weird for a looong time. My birthday here at work still makes me anxious, we are not used to be fussed over. Even though I know it is fun and they like to make a big deal, and I like to do the same for others, Jiminy-christmas...it's hard to accept the attention after how we were raised.
I secretly loved the winter holidays years before I left...I like shiny sparkly things and tink-ly music. I started by buying calendars for the staff probably two years after I left. Now I'm in the full swing of things and have holiday doo dads all around. A day of reckoning will come sometime with my brother who is an COBE/elder. But he lives out of town and what will happen I think is that he will be disappointed. And there is no resolving that...either you get it or you don't.
I was lucky that a few of us who met here on the board about the same time started stumbling together on our first Christmases and holidays. We got to enjoy it and also talk about our feelings. We all like shiny sparkly things. In fact one year, a couple from here, Aude Sapere and I went to a Christmas evening celebration at a Unitarian church...don't even know what it is called. Then we had a late dinner after.
So my suggestion is to do what you like...it is weird at first, but if you enjoy it...it is lovely to celebrate everything. Yes, holidays are commercial, but if you enjoy the process...it doesn't matter. If you are uncomfortable or it's not your thing...just don't worry about it. You are free now.