How big are your hands? Upper fret access is one of the few parts of guitar where hand size actually makes a difference. I don't play that high up the neck too often anyway so I hardly notice.
Take out the jig saw.
Watch a recent video of Mick Box of Uriah Heep. He changes the position of his thumb for upper fret access. I'm not a fret wizard, but it does kinda help
https://youtu.be/TV77dfMQQ6c
Also check out the left handed Buzzard Bass, and drummer uses bike racing shoes.
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