After trying various others, I find Kaspsersky Free AV good on my Win7, although the updates tend to slow my 4GB down a fair bit for a few minutes [Er, actually it's just 2GB. Yikes]. Not too much nagging, but check when installing for the agreements - after the essential one (or two, I'm not sure now) it goes on to put up another two EULA that aren't essential and give them more permissions than you might like.
I'd say it's important to have something with live scanning, for when opening or copying files, and a good set of addons/plugins on your browser, rather than a routine monthly, weekly or even daily scan. When there's an infected file, you want it caught immediately, or it'll mess with the system before you've had time to find it, and getting rid of viruses is sometimes an enormous and complex task. Kaspersky has a browser addon for most browsers, I think (certainly has for Firefox). The other browser addon I'd recommend is UBlock Origin, which works pretty well out of the box to block security and tracking issues, blocking access to dodgy sites and stripping pages of dicey content.
Longer term, one of the problems with W7 not being supported is that other software providers also start to abandon it. I've kept my XP machine running for ages, but now just offline, and several programs I kept it for stopped putting out XP updates. Not a massive problem if you just stick with a version that works, but sometimes irritating if your favourite program is being developed and has great new features, but you can't use them without upgrading your Windows version.
Depending on how you use the system and apps, there's the other option of a dual-boot system with something like Linux, keeping Windows offline and only downloading what it needs via the Linux system...I've not learned much about what this would involve yet - I'm just working out options myself. I'm thinking it's time to abandon Windows and go full Linux, but it's a wrench losing a few pieces of software that it won't run (the same, even under Wine or whatever). I've got really used to writing scripts in AutoHotkey, for example, to make my computer do all sorts of things it wouldn't otherwise, and write whole programs, and I'll have to learn a new programming/script language for Linux, probably Python. Finally found the best note-taking, text-grabbing software, CintaNotes, only to find that doesn't have a Linux version either. Eventually, I'll get used to the change - I've dabbled with Linux already.