Just switch to W10....Life will be easier...
You need a reasonable network solution, which means a robust and reliable firewall, and this is often solved by using a router that isn't set to lax defaults.
Internet-facing element - keep your browser up to date.
You could also switch to a different email client - e.g. thunderbird, and maybe a 3rd party media player - vlc or whatever you fancy.
Make backups of the os and data regularly - plenty of programs to do that.
Run Simplix pack.
AV are an extra line of defense in case you stupidly let something through. The other stuff is more important. I expect Kaspersky is fine. MS will keep releasing definition updates for their oiwn MSE until 2023, so 3rd party soultions will keep supporting win7 for at least that long, I expect.
Browser with security add-ons, plus email client and media player. Anything that connects to the internet should be kept up to date.
The most important question to define is, secure against what?
What worries you?
W7 is no longer SUPPORTED by Microsoft...There are no security updates for it any longer except for MS essentials. Any W7 vulnerabilities that show up are no longer being fixed by MS..
You are asking for trouble if you keep using it..
That is false information.