Well avast is the most flexible, configurable AV that I have ever used and I've used a few. Not to mention it is relatively light on resources when compared to the behemoths out there.
Should you chose to try it, ensure that you uninstall (not just disable) your existing AV (especially if it is NAV, let us know as this often leaves stuff behind), two resident AV are likely to cause conflict rather than twice the protection.