I want to keep my c5400x as my main router and add a few deco M9 plus as acces points

Here are my questions:

1.Can i buy single additional deco m9's and add them as acces points or do i need the deco m9 plus router also?

2. If i use the deco m9's as acces points only, do i loose the mesh functionallity with that zigbee function for example?

Looking forward to the answers and solutions