I have a GK Backline 600 and it has a footswitch jack for switching between channel A and B Will any 1 button footswitch work? Something like this maybe? Fender 1-Button FootSwitch (099-4049-000) https://www.amazon.com/dp/B001L8NGJ2/ref=cm_sw_r_cp_api_e66bAbCN1V1W4
From the manual - "15-Footswitch /A/B: ¼" jack for a standard single pole latching foot switch" That footswitch would work if its the 'latching' type.
I would take the "latching" requirement to mean you step on it once and the switch closes. Step on it again and it opens up. Step on it again and it closes again, and so on.