Depends on budget, what connections your TV has and what media source(s) can output (Dolby Digital, Stereo ATMOS, etc)

“Great” setup

1 x Sonos Arc (for under TV - Centre, Left, Right and height)

2 x Sonos One SL (Rear surrounds)

1 X Sonos Sub

“Very Good” Setup

1 x Sonos Beam (for under TV - Centre, Left, Right)

2 x Sonos One SL (Rear surrounds)

1 X Sonos Sub Mini

I vote for the @BMF "Great” recommendation above.

I do have a family room about the size of yours, just slightly narrower, and my setup matches the "Great” one:

• 1 x Arc
• 1 x Sub Gen 3
• 2 x Symfonisk (IKEA version of the Sonos One SL)

The result is indeed “great".

You would ideally place the Arc under your TV, the 2 One behind your viewing position and the Sub somewhere (the position not being as relevant). Ideally, the Arc would be centered in the room in order to have the side firing speakers project at equal distance laterally.

With a room that size, I would go with the Sonos Arc + Sub + One SLs as surrounds (if you can afford it, go with the Fives as surrounds). And get a Sonos Port or Five so you can connect your turntable. If you have 8-10 foot, flat ceilings, try to place your main listening position about 7-9 feet from the Arc to hear the upward firing drivers when playing Dolby Atmos content.