Option number x is a
Dual WAN Router. This is a single device that you can have 2 different ISP connections and this will give you a Failover if one ISP goes down. It doesn't help if the phone exchange is the culprit that has the issue as both ISPs will connect to you through the same exchange. It will also require 2 Modems (one for each ISP) but the Dual WAN Router will handle DHCP, DNS and anything else you may need configured.
Read the link I have left I the first sentence as that explains it better than I can while my present visitor Ian Somnia stays for an unwelcome visit.
Google Dual WAN Routers. This may help you research this option further. This type of router is still a single point of failure if the device fails but it does save having to configure 2 different routers that you would need for 2 different ISP connections.