Simple solution: subcutaneous key implant. Someone has to physically cut you open to decrypt your notes. Hopefully your attackers are not too determined... but

Simple solution: subcutaneous key implant. Someone has to physically cut you open to decrypt your notes. Hopefully your attackers are not too determined... but then again, any system where your death results in decryption has that particular flaw. A bigger problem is if you die in such a way that your body can't be recovered.