The safest way to store a private key is to store it in a cropped form, and keep the missing part in your head..
Imagine that this is your entire private key:
prizm opposite crimson both shower precious hopefully here keep trace barely many upset give image scream movement peaceful reveal
Remember last 2 words:
prizm opposite crimson both shower precious hopefully here keep trace barely many upset give image scream movement peaceful reveal
Delete these 2 words - and store in this form on electronic media:
prizm opposite crimson both shower precious hopefully here keep trace barely many upset give image scream movement
( Don't forget about SPACES between words - they are also part of the key )
When you make a transaction, you will need to copy and paste the first part of the private key and add 2 words from memory, taking into account the spaces.