If Windows Defender doesn't do it for you and you're super paranoid, then you can try a cloud based anti virus like Panda Cloud.
Just have to make sure you have a solid connection to the internet and it will protect you in real time using virtually no resources on your PC because all the action happens on their end and just uses your connection to the internet to remotely scan your computer and protect you in real time while web browsing.
Probably your best option for a 3rd party anti-virus on such a low spec machine.
But again, Windows has their own built in anti-virus called Defender and it works pretty well.
Consider CloudReady, a community version of ChromeOS, it performs very well on low-end hardware. The Intel Core M was pretty much abandoned by all manufacturers the year after it was released since it could not handle running windows very well.