Would this work for you?
https://www.amazon.com/dp/B000MNBWW0/ref=cm_sw_r_cp_apa_i_OEuEFb4ACJS47
It wouldn't require an electrician, and since it is automatic, you might be able to rig up an autostart signal to your generator if it has autostart input, to have auto back up. Otherwise you could just start the gen when you need it.
Yes, 2 large UPS systems would be the best way to do this.
You can use a 1U ATS for devices that don't support redundant power.
https://www.amazon.com/Tripp-Lite-100-127V-Rack-Mount-PDUMH15AT/dp/B000MNBWW0/
edit: the cheaper, but not recommended approach would be to run A leg power from the UPS/generator and run B leg power from dirty (unprotected) power. This way your single UPS doesn't become a single point of failure.
The lower end Tripp Lites are significantly less expensive
https://www.amazon.com/Tripp-Lite-100-127V-Rack-Mount-PDUMH15AT/dp/B000MNBWW0