My Mum is no longer here either and physically I wish she was. She would be in her glory with the 6 grandchildren she now has - and probably spoil them rotten. But she is here, in spirit. Of course I can't prove that scientifically, but it's been proven to me on a personal level and that's all I need.
My best is just watching the faces of the kids and the dogs - itsn't it amazing how dogs and kids gee each other up? Maybe niether fully understand the 'true' meaning of Christmas, whatever that is, but their honest happiness and sheer energy is addictive!
All of this does bring back memories of course, both happy and sad. So Christmas is probably bitter-sweet for most of us. I think one tip that might help, I know it does for me - don't feel that because you haven't got a permanent grin on your face or that you are not ecstatic about Christmas looming that you are not in the spirit. Christmas is and should be a family time we all know that, but it is also a personal time. Being human we rarely feel 100% happy, that is part of what being a person is, and the bag is always a mixed one, you can't just switch feelings off just because it's Christmas. Accept how you feel, accept that it is natural and you won't find the prospect of Christmas so daunting. Love and best wishes!