Tried the free av/ firewall route and regretted it. Ended up with Kaspersky Internet Security. Expensive but worth it imho.
I also have the operating system its own partition and keep the data on the rest of the drive. C: partition gets cloned regularly to the second partition just in case. Second partition gets backed up to second (external drive) - if travelling would probably get backed up to DropBox or similar.
Having caught a virus once I do NOT want to get caught again. After several wasted days the only way to get rid of it was to restore a previous copy of the c: drive. Fortunately, because I keep my data on the second partition it was not affected.