Why haven’t I done this before!?
I was home one evening talking about my work and I was reminded of using a projector to project shapes onto the canvas to get proportions right etc.
SO I found an overhead projector – I chose this instead of a digital one because I can still hand draw the shape I want to project onto the painting.

Acetate proved the best paper (not greaseproof paper which I originally tried). This is the drawn shape, based on a photo of the sculpture and the most successful sketch in my sketchbook.
The I projected it onto the painting and traced the white lines on top! This made my life so much easier omg.

The result is so much more exact than the previous two paintings. I’m going to use this method from now on!
The thing I need to refine now is how I draw the sculpture – how far do I reduce the shape down to single lines? Here I think the structure is too curvy and complicated.