You could always have it memorized.
You could also go on your mobile, to the notes app probably already installed on your device and have it written and stored there. Then safeguard it all with a password or whatever security lock your device uses.
These are probably the things which we should avoid while safely keeping our seed phrase and you are going the wrong way.Do you think the human mind is capable of memorizing the 12-24 words in complete order for whole lifetime? You could easily mess that up and brute forcing will not be an option to you.
Storing it on notes on mobile is risky as what if your phone is lost? Your seed inside your phone will be used to take out your funds by importing it to any wallet that supports BIP-39 and then you will regret.Any security lock on it is breakable as it's easy to do such things so don't go this way and prefer offline modes only.