Split your nsec into a multisig

The keys of that multisig talk to each other over nostr to sign notes

nostr:nevent1qvzqqqqqqypzq90tw8h09v4m9t4929cjwu9a2npp53mrp4um4fcxrgx7gq437ftfqy2hwumn8ghj7un9d3shjtnyv9kh2uewd9hj7qpq06wkzsm2p0ug7ul4gn9kp54xdqvv7vuc3w24qpccz99c6x86lumqq0a9s9