Now i've just switched to linux, and i'm not sure what to get - are there even many virus threats on linux????
There aren't any viruses for Linux, so you don't need to worry. However, there are antivirus apps for Linux that are mainly for scanning emails so you don't accidentally forward viruses to Windows users. The best of these is the open-source ClamAV. It can be set up to scan all emails that go through your local mail server, or you can just use it on the command line to check individual files.