ARoarer-
Unfortunately I was raised as a JW so I never got to experience Xmas. That's probably why I go overboard now.
I'm so sorry you missed out on celebrating with your mom. We all have regrets of things we missed out on because of being in the org. I don't know what your beliefs are now, but if you feel that your mom is in heaven (or still with you), then having a tree may be a healing thing for you. I think decorating the tree (maybe with some of her ornaments) might help you overcome some of the guilt you feel.
As far as worrying about repercussions, that's something you have to decide. I remember the first Xmas I celebrated I was constantly looking over my shoulder when I bought decorations. Now I don't really care. Like you said, you can't have the fear of man. If you want to put some lights out, then put some lights out.
Personally, I love everything about Christmas. The sights, the smells, the sounds...I don't even care about the gifts (other than the fact that I like to buy for other people). Bottom line...do what feels right to you, not what you think you should do.
mom