Why not adding a Anti-Ransomware solution next to the AV of your choice?
I would recommend
CheckMAL AppCheck AntiRansomware Free, it comes with Behavior Blocker, Auto-Backup (limited to preset), Remediation of affected files, MBR Protection.
Free and efficient against most ransomware.
Make sure to have a backup anyway in case a malware of a system / hardware failure cripples your system. Don't attach the external HDD to your running system unless performing / restoring from a backup, it will be targeted by malware otherwise.
Product Introduction - CheckMAL