I use oat milk or almond milk 2 to 1 ratio (1 cup “milk” 1/2 cup oats) and then add 1/2 cup of either pumpkin puree or applesauce depending on the exact flavor I’m going for. I add in ground or whole flax and chia seeds and it thickens up nicely. Add berries or banana or seeds/nuts ahead or when you eat it, just changes texture a bit. I also put a little bee pollen in morning of to add texture.
Have also experimented with adding instant arabic coffee - it was delicious