I use AVG free.  Occasional ad's don't bother me.

I also have Malewarebytes free version and boot into safe mode to run it once or so a month.

I started using a modem and joined the Boston Computer Society many years ago, that was before the Internet.  In all this time I've had 1 (one) virus.  A friend said look at this and it was a fireworks display with a virus.  That was long ago and was easily dispatched with the Norton product at that time.

Rules: Don't click on links in emails.  Don't click on links to see how to get something free.  Don't go to porn sites.  Don't open emails in anything other than text mode IF it's from a business you think you know or do know but have no reason to believe they'd contact you.  Don't have your email open automatically when you click once on it.