Paper backups are the best option for this. Private keys are simple enough that a whole wallet can be printed to a single piece of paper using an OCR-friendly font.
I wouldn‘t send it to a printer (and certainly not generate the passphrase on a computer that is connected to the internet). Write by hand, it is only 12 to 24 words.
A copy could end up stored on the printer's hard drive. Figuring out whether you have a printer where that's possible is more work than writing it by hand.