VRRP [0] is what you're looking for if you want to minimize failure points and manual actions. This allows multiple devices to "share" ownership of an IP address, giving you a single gateway address you can point all the clients towards. The protocol can detect when the current active device is unresponsive and transfers ownership of the IP to an available device. VRRP can be used on Linux via keepalived [1].

Setting all that up with a couple Linux machines would require some networking knowledge, but there are tutorials out there for all the pieces you'd need to put together.

[0] https://en.wikipedia.org/wiki/Virtual_Router_Redundancy_Prot... [1] https://www.keepalived.org/