A big culprit for swaying the hips too much on the backswing is the movement of the left knee. The main reason for the left knee to move too much on the backswing is because of incorrect sequencing. The correct sequence we want to have happen in the golf swing is for the upper half to start first followed by the lower half. When the left knee starts to move too early it simply means that the lower half has started first.
The first thing we need to do is to make sure the upper half goes first. When starting your swing focus on moving the clubhead first. Once the clubface reaches your right foot, then start to allow the hips to turn followed by the left knee. If you do this in this sequence you will greatly reduce the left knee movement and feel more control of your turn on the backswing.
Also when the club does reach your right toe, focus on turning your right hip back with the pressure staying inside your right foot to ensure the hips don't sway. Once done correctly this will further reduce the movement in the left knee. Lastly a great way to assist in having the correct feel is practicing setting up with your right foot behind the left. Again focus on moving the clubface first followed by your hips and you'll find with this drill that you will stay very controlled over the ball.
When analysing all movements of the backswing. The correct amount of turn for the left shoulder is 90 degrees followed by the hips at 45 degrees and then your left knee at 20 degrees. There are times however I would be in favour of more left knee movement as long as it didn't compromise the turn of the body. People who are golfing later in life can be useful as well those who have restricted hip movement.
If you'd like an further help in reducing your left movement just let me know and we'll book in a time.