Do I need a router (netgear, etc.) and if so, what kind?

Hi. We have a netgear router and it has been working fine, until now. Suddenly, we can't stay connected and have lots of interruptions. OR we can use the internet for some things, but not others. We switch back and forth between that connection and our Comcast/Xfinity, but it too doesn't work regularly, and not on all things. For example, it isn't strong enuf to reach to our garage, where our sprinkler system needs it. Do I just need a new router? Or a new modem? Can't get a human on Xfinity, so I'm trying this route. Sorry, i'm not technical so I may have described this poorly.

Any assistance welcome. Should by Xfinity equipment be sufficient? 2000 sq. foot house.