I recommend the Trezor, or The Air gapped cold storage set up.

Both guides below follow the same general set of principles, and can be replicated for most other cryptocurrencies.

Air gapped Cold Storage Guides ⬇️

Bitcoin:

https://en.bitcoin.it/wiki/Cold_storage

Monero:

https://www.monero.how/how-to-safely-hold-monero-in-cold-storage