For your buttering, what is your goal? It seems like you want to tail press to switch? Or just aren't countering the slope of the hill so you rotate.
If you want to spin 360, it helps to do a setup carve and carry the rotation through as you butter. You can then move to continuing to rotate around all the way down. I prefer a 360 or two, then 270 out.
Second thing, think more about shifting your hips back instead of your whole upper body. So you bring hips back, but keep the upper body straight. It helps to keep your balance and let's you get lower so you get more height but still be stable. This is even more important for a nose press down the hill. If your lead shoulder comes too far over the nose, you will probably crash.