I am indecisive about choice due to room size

Had a friend who worked at Stereo 
Exchange in New York . He once told me being able to have any system he desire , that the most important thing in a Audio System setup was Acoustics . Work on the acoustics of any particular room then worry about the hardware . That up to 70% of what you hear in a particular system is the sound of the room .The good thing of working your room is you do it only once . You can upgrade this or that of your system but what you did for the acoustics of the room never changes . Take care and be safe .

That up to 70% of what you hear in a particular system is the sound of the room

Absolutely!! Until you treat it, you can't hear anything. 
What I think happens is that over a long period of time, Audiophiles learn to hear past the room acoustics, but it's like watching a movie in a smoke filled room. 

I can also say that I've gone through a lot of hardware, but I've NEVER played merry go round with my room acoustics.  I've only added more pieces.

Test for you.  Sit 2' from your speakers and listen to them.  The difference between that and your chair is room acoustics.

Re: Speaker upgrade- What sound are you looking for? Why the want to upgrade?

If you have the cash to upgrade the Naim as well, your choices are sound. Speakers?

Have you considered a subwoofer with your existing Sonos Fabers?

I wouldn’t over sound the room...
cheers 🇦🇺

12x12 x 8 is limited,,,12x12 with say a 16 ft ceiling, now you have options.

Options?   Turn the room on its side?