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Just buy 2 simple cheap flash drives. Create some excel file on it. And write all passwords and keys in it.
Make copy to second flash drive. Don't do ALL what you was read in Internet. If you will write this by pencil on your paper, one day you lose it. Because all people make mistakes. Copy&paste method never make mistakes.

Sorry to hear your story @michaelwilshaw
It would be even more painful if neo become more expansive.
Anyway what you can do now.
For longer private key, I use a formula. At first I write all letters from left to right then again write it down right to left and cross check again if they match each other. You may follow this rules. I hope next time you will not lose any crypto.