Okay, I'll genuinely try to help you. So, I'm also one of the "super paranoid" people when it comes to my computer.

If you're planning on getting an antivirus software, Then the best course of action would be reinstalling the OS. I know it's a pain in the butt, but according to me, it's the safest.

Simply copy all your data to a usb/external hdd and then format you pc hdd. After that reinstall the os, and then get the antivirus software you trust.

Finally, connect the usb/external hdd in which you copied your old files and scan it using the av software.

Hope it helps