Whole-wheat option: replace 1/2 cup of white flour with 1/2 cup whole-wheat. The cookies will be too dense if made with 100% whole-wheat flour, unless you use whole-wheat pastry flour.
Dairy-free option: substitute butter for coconut oil.
Vegan/egg-free option: substitute the egg with 1 tablespoon of ground flax mixed with 3 tablespoons of warm water. Mix and wait until paste forms.
Gluten Free: substitute regular flour for a 1:1 gluten-free all-purpose flour.