a multisig where one key is trezor, another is on a secure, identity-verified web service, and the third is with the wallet provider
for my cold savings the trezor and its seed would go into a safety deposit box
my spending/income coins would also be handled by another trezor that stays at home in my home safety deposit, from which i transfer into my smartphone hot wallets on regular intervals. the seed for my home trezor would also go to the bank. income designated for savings would be shipped off to my ultra cold trezor also at regular intervals