I’ve thought about seed and password backups before, but it’s hard to find a balance between never losing access yourself and never allowing unauthorized access. Ideally, backups would be protected against both physical theft/loss and spontaneous memory loss.
You could duplicate your wallets across multiple devices, as you mentioned, but if somebody steals one of your hardware wallets and it’s not password-protected, then it’s game over. If you add a password to your hardware wallet, then we’re back to the question of how to securely store that. It’s hard to remember infrequently-used passwords.
You could use multisig wallets, but most cryptocurrencies don’t natively support them, and they aren’t useful for backing up passwords, so it depends on your needs. You could still lose access to a multisig wallet, but it is more robust against loss/theft.
You could instead use an algorithm like Shamir’s secret sharing (SSS), which also allows you to store arbitrary data (such as a backup of your password manager’s master password), but requres running software to recreate the encrypted data.
One of my favorite ideas is to leverage the one-time pad (OTP), which is the only 100% cryptographically secure encryption technique (as far as I know) and is also easy to do by hand. This allows you to recreate arbitrary secrets without relying on software (as you would with SSS or other techniques). You just need a source of entropy to produce randomized characters, which can also be done by hand (be careful to do it properly). You could then duplicate the secret key and ciphertext and store them in various locations.
However, wallet duplication, multisig wallets, SSS, and OTP all require you to store things in multiple physical locations, which adds more complexity than most people would be happy with. Although for SSS and OTP, some of the shares/copies could be stored in the cloud.
You could also use two dedicated password manager accounts with a provider that supports emergency access. One account can store your secret and be locked with a long, random password, while the other can have emergency access to the first. The second account’s password could be written down and stored without much care, since you would get a notification and have days or weeks to prevent the thief from gaining access to the secret(s) you’re protecting. If security and access are both of high importance to you, I personally think this is the easiest option for most people. It also means you only need to buy one hardware wallet. Do be wary of providers shutting down your account due to lack of use over longer periods of time - although you could duplicate this setup across multiple providers to protect against that, too. Also ensure you’re paying attention to the notifications, perhaps even forwarding them to multiple people to guarantee somebody you trust will be notified of the theft.
