Encrypt the private key with a strong one time password which you print off (multiple copies) and put in safe places. This is perhaps not ideal perfect securit

Encrypt the private key with a strong one time password which you print off (multiple copies) and put in safe places. This is perhaps not ideal perfect security, but ultimately security is a always a tradeoff with usability and losing a physical item probably has greater chances than someone deliberately trying to get your private key.