Windows 7 will not be updated.
But, if you have no problems now, you are unlikely to in the future.
Security updates are mostly done to the apps you use.
Windows defender/security essentials was recently tested as one of the best antivirus products.
https://www.techspot.com/news/81396-windows-defender-ranked-joint-best-antivirus-program.html
Defender is very good at spotting known viruses.
More sophisticated products attempt to catch "in the wild" viruses which have never surfaced before.
Such apps take more resources.
Most security issues enter via social engineering.
You click on a malicious email link for instance.
If you are prudent, you have little to worry about.
Above all, you need a form of EXTERNAL backup.
Not just for viruses/ransomware, but for things like fire or hardware failures.
Your main reason to have to move to 10 is for support of newer technology.