[Mashiro]

If you are using Windows 10 the latest Windows Defender is already a good free solution as an alternative to other free AV software. In the last years Windows Defender has leveled up in quality, detection rates and other factors. It is already built into Windows and doesn't require any additional installation. The resources usage is absolutely alright and won't take a big hit in performance on a normal modern system.

Another free alternative is Kaspersky Free. Kaspersky is up there in the major league of AV software. The free version comes with enough essentials to protect the computer from viruses. Resource wise it is also alright. --> https://www.kaspersky.com/free-antivirus

If you have money to spare I would recommend ESET NOD32 Antivirus. It is one of the best world wide and has a little footprint and barely any performance hit.