MESH help please? - eviltoast

Hello!
So I am looking to buy a MESH sytem but I want to ask a question about my home network, if anyone can help me.

So I have a Modem/Router at my balcony, which has 3 ethernet cables connected:
A) Through the walls, ends up at living room
B) Though the walls, end up at one bedroom
C) Connected to an ethernet switch, which then has another 8 ethernet cables connected

I have read that the 1st Mesh unit must be connected DIRECTLY onto the modem/router. But I want to connect the 1st unit at my living room ( so look option [A] above ). Will that work? If directly means literally next to the modem/router, I will have to leave the 1st Mesh unit at the balcony which is really not possible, I am going to waste most of its signal.

Any opinions welcome!

P.S. Right now I am using an Access Point at option [A], and an Extender at option [B]