Functional testing and site availability monitoring service with notifications?

Question

Software testing

The task is to set up automatic testing of the resource and receive notifications in case of failures.
Need to track:

1. Functionality (some button does not work, registration is broken, etc.);
   
2. css and layout errors (for example, the block "left" after the next code update);
   
3. Violation of cross-browser compatibility, including on different platforms and resolutions.
   
4. Site availability
   

I see solutions:

1. One of the options:
   
   • Selenium + Saucelabs
     
   • ghostinspector.com
     
   • pingdom.com (they have a test editor)
     
   
   
2. In ghostinspector.com you can set the % "similarity" of the result of this and the last test result
   
3. manual verification via Selenium + Saucelabs or separate services (browsera.com)
   
4. Pingdom and similar services
   

Is there a better solution to the problem at hand? What are you using?