PSA: If you're buying bitcoin for the first time, do not leave it on an exchange. Please take self custody

If you have an offline computer that never connects to the internet, download Electrum or Sparrow wallet as a standalone and run it on the device.

Be sure to then get yourself a hardware wallet.

Coldcard

Jade

SeedSigner

Passport

BitBox

If you manage to acquire a good understanding of key management, which you should care about acquiring, then you can boot Tails OS on a USB, run electrum offline and use a watch only wallet to broadcast transactions from an online device. It's essentially a cold wallet at zero cost but requires some technical knowledge.

Your cold wallet is your savings account. You can top up a hot wallet/lightning spending wallet (your checking account) as and when you need. Recommended lightning wallets, Alby, Breez, Phoenix, Zeus and Muun wallet.

For collaborative custody and Bitcoin native financial services, check out Unchained Capital.

If you're looking to buy bitcoin without KYC, look into Bisq and Robosats.

A lot of people who are new to bitcoin think taking self custody is complicated but it's not. Backing up 12 words (and maybe a passphrase for plausible deniability) should not be complicated for anyone who passed primary school. It's never been easier for us to truly "own" anything without counterparty risk.

Adding a strong passphrase to your seed words is like a dual key setup if there's no single point of failure for your seed and pass phrase and they're stored separately. You could also consider steganography.

Further reading:

Ultimate guide to storing your bitcoin seed phrase backups

How to secretly travel with bitcoin using Steganography