I'm very sorry for your loss. I know what you're struggling with. An inordinate number of our family members passed on between Thanksgiving and New Years day. I have come around to the opinion that they would not wish for us to dwell on the sorrow and they would rather we have the happiest of holidays.
My grandfather was really into trains. I can't hear a train whistle without thinking of him. Last year (several years after his passing), we started slowly adding train ornaments. As they start to accumulate, we may end up with a train-themed Christmas tree at some point.
I wish you the best.
Then the Grinch thought of something he hadn't before. What if Christmas, he thought, doesn't come from a store. What if Christmas, perhaps, means a little bit more. ---Theodor Seuss Geisel a.k.a. Dr. Seuss