I'm a lefty and I struggle with many of the things you are. My main focus this year is to stand tall, front foot pressure and try to stay in alignment. Coming into my off side turn I tend to reach forward and bend at the waist. For me it's what I call a safety move. My eyes (and upper body) tell me I need o stay with the ski through the turn, I'm anticipating the finish of the turn, the load of the boat coming and I do some not so fundamental things coming into the turn to make the finish manageable. Some of it has to do with not being in skiing shape. But the result is a stall, a loss of angle, slow acceleration off the buoy, all of the above, flowed by a panic move to get into my stack. Or the best stack I can muster up.
The turn for the gates has to be on the front foot, with some speed, a carve and a lean away. It is not a slow roll, falling back on the boat and on the back foot. A windshield wiper turn if you will. You offside turn should be very similar.
This video below is of a lefty. It may look like some scrappy skiing at the end of his turns sometimes but the line lengths are pretty difficult at that time. The one thing about this guy is, he never looses his hips.