Maybe Pause key could be used for legacy "Ctrl+Z" and "Ctrl+Break" for Ctrl+C

That would require moving your right hand (potentially on your mouse) and anyway too far away and not even present on laptop keyboards...

Maybe you could use thumb+Escape for Ctrl+C?

Or thumb+X is simpler - you can't cut anything in the terminal, so "cutting" the current process is a convenient combo and even has some mnemonic potential

You could also have +C copy when text is selected and break otherwise, though that modality can be a bit confusing / error-prone for some