Carlson Extra Wide Walk Through... https://www.amazon.com/dp/B000JJDI0G?ref=ppx_pop_mob_ap_share

SureFlap - Sure Petcare Microchip... https://www.amazon.com/dp/B003EGIM3O?ref=ppx_pop_mob_ap_share

I removed the cat door on the gate and the sureflap fits the opening allowing 1 cat free roam to entire house while the other is confined to 1 level.