I've been using Windows NT6 (Vista and 7) with nothing but the free and excellent Microsoft Security Essentials and the included Windows Firewall for years, with zero problems. (XP is a different story and should be dead by now)
The key IMHO is to NOT use Internet Explorer if you can avoid it. Chrome and Firefox have their security holes, but they are inherently much, much more secure so it's far less of a real-world issue, and you can have things like adblock and NoScript (blocks javascript unless you allow it) that render you virtually bulletproof.