Your not applying pressure to the front of the ski to turn at all, you see it on the snow (or lack thereof) coming off of the the ski. The reason you bend forward (upper body) is to try and apply this pressure and your bum sticks out to compensate. Press a little with the knee (shin) and bring the shoulders back, bum will automatically come in. Easy way is to relax and ski upright resting slightly on the shins as you ski, the balance you ultimately achieve (ideally neutral) will be the better (upper body closer to vertical) stance. The still photo you provided clear shows an almost vertical lower leg. This video also shows a slight slide in the tails indicating wt slightly back (again bum sticking out)
I agree with EPIC slide slip, both directions 10 to 20 feet each side, each run. Try to slide without dropping tips or tails, and without drifting front or back. Not as easy as it sounds. You'll notice the difference in both stance and turns once you hit that neutral point. (Still do this a couple of times everytime I ski, instant feedback, instant correction, instant neutra, perfect balance).
You're trying to the right thing with the wrong body parts.