Which are the best free ones?

A cold wallet is a secure method of storing cryptocurrencies offline, reducing the risk of hacker attacks.
There are two main types: hardware wallets, such as Ledger or Trezor, which are physical devices where private keys are protected, and paper wallets, which consist of a paper where the public and private keys are printed.
To have a cold wallet, simply purchase a hardware wallet from a reputable manufacturer, set it up following the instructions and write down the seed phrase in a safe place, or create a paper wallet with reliable tools. Then, simply transfer your cryptocurrencies from the exchange or hot wallet to the cold wallet address.