This a good explanation on how to proceed.

https://packetpassers.com/multiple-isp-connectivity-redundancy/

This how to set it up

https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClElCAK

These are firewalls to buy. Fort iNet looks like the best to use for dual isps because it offers load balancing to get the best signal and quick switchover.

These are the ones to buy/choose.

https://www.allconnect.com/blog/the-4-best-hardware-firewalls-for-home-wi-fi