- https://firebase.google.com/docs/perf-mon/get-started-web (this is a new feature released by Google. Luckily you don't need Firebase to use this. https://www.youtube.com/watch?v=KYYjdWSrRjI&t is a good tutorial on wiring your app up)
- https://reactjs.org/docs/perf.html
- lighthouse by Google
You could just run lighthouse on your app periodically for an in depth audit on your site. That way you wouldn't need to slow down your builds with a test (not sure what's best practice here. Just trying to throw out some basic ideas)