Yes. I would suggest the good and lightweight MSE: Spyware Protection | Free Spyware Protection | Microsoft Security Essentials
It is actually more wise to not pay for an antivirus when many of the free ones perform just as well as paid for ones. And they do perform just as well. Another good idea would be to install malwarebytes beside it for an extra weekly/monthly scan without any conflict between them whatsoever. All free.
Don't forget to keep updated: Windows, Add-ons, and the browser you use. Do this, and you are protected from more than 85% of all viruses out there.
Some programs contain vulnerabilities, such as MS office. Best to just keep all programs updated as well to further protect against this threat. And as you said, a wise surfer is a safe surfer.
Hope this helps