Bitcoins offer the possibility to store them by yourself. You are de facto your own bank. This brings responsibility which you must always be aware of:
> There is no one who can reset your password.
> If you no longer have access to your keys no one can help you.
This is not a problem as long as you take care of the storage of the important data in a serious manner. With today’s wallets this is also very easy. Most wallets are so-called deterministic wallets. With these all private keys are derived from a master key, the seed. All generated private keys of these wallets are related to each other and can be recovered with the original seed. Depending on the wallet, a seed consists of 12, 18 or 24 seed words (a seed phrase). With this seed phrase the wallet can be restored at will. Be careful, whoever has this seed phrase has control over the coins. The backup of this seed phrase must therefore neither be lost nor fall into unauthorised hands.
A good backup must therefore fulfill various conditions:
No keys or coins may be lost.
It must be protected against unauthorised access.
Restauration must be simple.
It must be findable.
It should not become unreadable due to external influences.
It must be as imperishable as possible.
It must not be dependent on a manufacturer.
How do we make a backup?
If you store the seed words as a whole you run the risk that whoever gets hold of them will have access to the Bitcoins. Many wallets offer the option of an additional passphrase. In addition, there are now wallets that enable cryptographic splitting (Shamir).
If this is not the case you can also do the distribution by yourself.
A first idea would be to split the 24-word seed phrase into two different parts 12 words each. You keep one half at home and the other in a safe deposit box at the bank. That is not bad but you can not lose one half. There is an even better option. You split the words in such a way that you have three backups with 16 words each and can put together the complete seed with any two of the three cards.
Now you are already on the right track with this backup method. However, written paper is only moderately resistant to environmental influences such as fire. If you want to be on the safe side choose steel or titanium for the seed backup. There are also various solutions.
A good Swiss solution is hodlr.swiss .