I've made the difficult decision to redo Minty from scratch.
This is partly due to the recent discovery that changing a sprite's size after designing the skeleton really messes things up, partly so I can add some nice-to-haves, like a view from the back for going through doors and different hand poses, partly so that I can leave space for future enhancements (such as extra facial expressions) and partly so I can fix a couple of minor weird issues, like the way that objects appear to pass through his arm when he holds them. I might also move from black outlines to a more modern style of making outlines a darker version of the base colour of the item they're outlining, which does tend to look better.
He'll look the same in the end, but the sprite sheet will be better optimised and easier to expand in the future. He'll also be in the proper scale, where 1 Unity unit will equal 1 metre.
I'm keeping the old Minty as well so that I can manually copy the animations I already made.
It's annoying and time-consuming, but I think it's important for the longevity of the project to do things right at the beginning. This will also help to improve my graphical workflow going forwards.