To me something else is going wrong in your network. Conbee II should support 200+ devices and if there are additional routers (repeaters) whole Zigbee network can support 65000 devices easily. I personally have now 90+ devices also connected via Conbee II and deconz integration, no additional repeaters and everything works flawlesly. Please note that most of mains powered devices (bulbs, smart plugs, etc) works as repeaters, so unless very specific case (large area to be covered or extremely high number of battery powered connected devices) there is no need for dedicated repeaters.
Have you checked this post? It provides comprehensive guidance to troubleshooting Zigbee network.