The Three Layers
Exchange custody (Coinbase, Kraken): easiest, fine as a fiat on/off-ramp, but 'not your keys'. Hot wallets (mobile/browser, e.g. Trust Wallet, Rabby): you hold keys, connected to the internet, right for transfer amounts. Hardware wallets (Ledger, Trezor): keys never touch the internet — right for anything you'd hate to lose.
A Practical Betting Setup
Keep your long-term crypto on hardware. Hold the month's betting bankroll in a hot wallet or on your exchange. Move week-sized amounts to the betting site as needed. This caps every category of failure — site insolvency, exchange freeze, phone theft — at an amount you predetermined.
Seed Phrase Discipline
The 12-24 word seed phrase IS the wallet. Write it on paper or steel, never photograph it, never type it into any website, never share it with 'support'. Every wallet-drain scam ultimately reduces to someone obtaining a seed phrase or a malicious transaction signature — slow down whenever either is requested.