I could never not have a christmas tree!!
When I had 6 cats, I used unbreakable ornaments, and tied the tree to the walls (I put the tree in a cornor) with fishing line. I also tied (not hang) the ornaments on (wrap those hooks good and tight around eash branch)
no tinsel, and lights only on while someone was home.
Also black pepper or ceyenne pepper all over the tree skirt
also applying some real minty toothpaste to the base of the tree itself helps to stop the climbing.