If you do not wish to write your passphrase in anywhere in fear of compromising it try to make a rhyme or poem with it only for you.
Mnemonic phrase usually some random word so give them a meaning so that you won't forget and do not tell it to anyone. Even if you write it down in some place no one will understand what is it if you do not tell them.
Trying to commit it to memory why having a paper back up is not a bad idea and does not compromise your security in any way, it could be another means of recovering if you lose your back up. This is also why you should have more than 1 back up in different locations.
- Jay -
I actually did that. I wrote down my seed words and hid it in two different location only I know. Also have an online backup but I don't think that won't be reliable cause anything online could be hacked or compromised. I prefer offline backup if you are sure you can store them securely.