For a 3200sqft 2 storey home, I am using Deco mesh - 3 M9 plus and 2 M5s.
I have a 1Gbps fiber connection and 4/5 Decos are on wired backhaul.
Works pretty well for my usecase.
I bet you can get away with 3 M9 plus or better yet 3 Deco X55 if you can get it from abroad.
I was having pretty good experience with the M9 Plus system but just that the network used to be weak on terrace and in balconies. So I added 2 M5s which resulted in all dead zones gone.