Yay, made it!
I settled in the end for a non-directional pattern and used a bottom fold (as it were ☺️)
OK it’s not perfect, and this is my perfectionist streak emerging, as the label is not exactly parallel to the side seam, so I guess my side seam allowance must have gone a bit awry, and I’m not happy with the stitching on the handles… But as Sazzie says it’s useable and that’s what’s important.
And I have another three cut out (from the same duvet cover, of course), pressed and ready to sew, so plenty more to practise on. And hopefully by number four I’ll have it cracked.