12 words is your wallet. Here is how serious people back them up.

Your seed phrase is your wallet. Wallet software, hardware device, list of addresses, transaction history: all derivable from the seed. Lose the words, lose every key, lose every bitcoin those keys ever controlled.

Three threats sit on every Bitcoin backup: theft, loss, coercion. The hard part is that defending one often weakens defense against the others. Keep the seed at home (no third-party loss) and you make theft easier. Use a passphrase to protect against theft and you can forget it and lose everything. Distribute shares to family to defend against coercion of any one person and any family member becomes a coercion target.

Paper is the floor. Pencil on acid-free paper, multiple copies in separated locations; fine for amounts under five figures. Metal is the standard for serious wallets; stainless or titanium, survives fire, water, and decades. Passphrase adds a "25th word" that produces an entirely different wallet from the same seed. The seed alone leads to a wallet with no funds (theft defense); fund the no-passphrase wallet with a small believable amount and it becomes a decoy (plausible deniability under coercion). Shamir Secret Sharing splits the seed into M-of-N shares; any M reconstructs, any (M-1) reveals nothing. Multisig moves you past single-key entirely; 2-of-3 with three different vendors means loss or theft of any one key still leaves your bitcoin safe.

There is no single best Bitcoin backup. There is the backup that fits your threats and amounts. Our newest addition to the rabbit-hole series walks the menu, with photos of real hardware (steel tubes, stamped plates, SLIP-39 share cards, multisig HW lineups), a embedded animation showing how 2-of-3 multisig actually works, and the tradeoffs at each tier. Down the rabbit hole:

https://www.learnbitcoin.com/rabbit-hole/seed-backup-strategies

Open source. Bitcoin only. No bullshit. Have fun.