We have three trees (sounds lavish, but two are small countertop ones) I’m not Christian either.
One has a Waldorf fairy that I made, one has a kinda kitschy jewelled starburst and the Harry potter tree has a winged gnome on top. You can put anything there! A star works well because of the shape, how about a felt (sparkly?) heart?
Pompoms are a great idea, we also have lots of felt hearts on our tree, they’re easy to cut and stitch while watching the tv- flat, rather than padded