Don't waste money on commercial anti-virus applications!
The maximum detection rate of any program out there in Windows is about 20%.
Even scanning a Windows system through clamav doesn't have a 100% detection rate. It's almost 100%, but not quite.
The only thing that you can do to protect yourself online, is to change your habits. Just don't use insecure closed source programs for things like online banking, going on the internet, and communicating. Keep the closed source software for free entertainment purposes, or when necessary for paid entertainment, but make sure not to make payments through the closed source software infected system.
By the definition of malware, almost - if not all - closed source software nowadays is malware. That's just how it is.
For some degree of real-time protection, the windows defender will do just fine when you're not going on the web with Windows, because it has basic firewall functionality that suffices for most users on a PC that's behind a router with a standard linux-based firewall built-in, which all routers have. You can check online for routers that are known to contain malware or NSA induced security bugs, there are lists out there, and never use a router provided by an ISP.
To regularily check for malware, there is only one way, and that's basically the way cloud service providers use, like Microsoft or Google or Amazon: with clamav. I've posted a howto for that on the forum. You can have the anti-malware power of Google on your PC for absolutely free, and it's really easy to do. You just use a live distro on a CD or DVD (not on a USB stick because those are writable and are also known malware vectors) once a week or so, and let it do a scan while you sleep.
If you really don't want to deal with malware, there is only one thing to do: dump that software console, and move to an open source real operating system. Not everyone is willing to do that because of the choice overload, they like to be told what to use instead of having to choose what they like best, so they just rather pay for someone else choosing for them, but for the people that really want to improve their lives, I can only recommend it. That doesn't mean that there isn't a reasonably safe way to use Windows applications anymore, for those musicians and gamers out there that don't want to miss out on windows-only games or want to continue to use budget-friendly music recording and production software with budget-friendly consumer hardware, because the gamers are held hostage the most, and musicians can use OSX, but that's another software console, which is safer and cheaper than windows, but it's still a 25 USD investment after having paid over a 100 USD for Windows already, and it's still a closed source software console with a closed ecosystem that can be classified as malware by definition... BUT, there is a HUGE difference between using a malware software console just for making music and getting entertained, whilst doing everything else on your computer in a more user friendly, more user centric, more secure, and overall more responsible way with open source software, OR allowing everyone and their dog to control your life, mind and possessions by using a closed source software console for everything.
It's very logical how it all fits together in the end: some people assemble their own PC's, and research the parts prior to buying them, so that they know what parts have known issues, what parts have compatibility problems, etc..., and they accept that they don't have a guarantee on the entire system, because they take their fate in their own hands. Other people pay a system integrator to build a system for them and make hardware choices for them, because they want the guarantee of the vendor on the complete system. If you transpose that idea to the software world, this basically sound consumer rights principle starts to make no sense at all, because in the software world, if you download an open source operating system, which is available for free, and which can be customized and selected after research, pretty much just like one would do research for hardware parts, you accept that you have no written guarantees, but you see that there is a huge followup of any possible problems by the huge and talented open source community, and since you can change at any time and you're not bound to a system, and everything is compatible with everything, there is no real potential for damage, WHEREAS, if you pay a company for a license to use a closed source software product, you don't get any guarantees at all, in fact, you have to agree with a EULA that says that you have no right of recourse against the licensor or manufacturer at all. From a logical standpoint, that makes no sense at all. If you would see sales conditions like that on a hardware product, you would never want to buy that product, you would probably refuse to even use it for free.
It's just a matter of taking a step back, and looking at the larger picture. Computer safety is a matter of common sense, and it's just not common sense that you pay for a product, and then have to pay extra for other closed source products to protect you against the dangers of that product you've bought. This is a risk and a burden that should not be on the shoulders of the paying customer. It's just wrong, however you look at it.