Special password books exist.

https://www.amazon.co.uk/password-book/s?k=password+book

Often people will mock them on social media for the likes, but actually in some circumstances ... I think they are the best option.

(They can be made stronger too - tell people to remember one word that they put in front of all their passwords but don't write down, like "cat". Then anyone who steals the book can't use it but they are still using different passwords for each site.)