My MAC has NEVER once got a virus. But then for 90% of the time I've had it I couldn't actually stay connected to wifi for more than 30 seconds due to unresolved issues with the device (classic Apple service). And whilst I'm pretty fast, even I struggle to get the gas mask on, the cable around...
Malwarebytes and one of the free antivirus products should do you fine (Avira, AVG, Panda etc). Check AV-Test website for some options, but I don't think there is much point paying tbh.
Caveat here is that you aren't going to very dodgy sites...
https://www.av-test.org/en/antivirus/