@Ihsan_H 

If you put the ISP router in bridge mode you can use one of your Deco units as a router straight away because they support router mode.

If you insist to have a separate router in your topology then use this FAQ In this case any router would do the job but it won't be in mesh with Decos. You can refer this FAQ as well.

Easymesh and Deco mesh are different technologies and they are not compatible - details.

In this case If your Deco system covers all your premisses just turn off your router wireless radio.