Hi Oggie,

It appears you are taking the club back too flat on the initial takeaway....leading with the hands too much. You need the shaft to be nearer the yellow line to keep you on plane.



Provided you are bent forward at the hips sufficiently the club should simply raise on plane as you let your shoulders and hips rotate (left shoulder turning down towards the ball and the club comes up). Simples

If your shoulders are approaching a 45° angle at the top of your backswing then the club will be nicely up on plane.... (below)



This guy is basically still in the address position with his hands/arm/club. All that he has done is rotated his shoulders and his hips... the club just follows. It's all about making the swing as simple and repeatable as possible.

Note: When talking about the right leg straightening - you don't have to snap your right leg straight so that it is locked dead straight, just allow it to straighten as necessary so that the hips turn a full 45°. Mine straightens quite a lot but it's not locked at the knee.