I bought a 1 TB Samsung T5 SSD for Time machine backups on a 512GB 15” MacBook Pro that I bought recently. With that and a Yubikey (with an off-site backup Yubikey of course), I’ve got everything I need if I ever have my laptop stolen or rendered inoperable. I’ve also got another older spinning rust external hard disk for backups, but that’s more of a backup of a backup thing.