Due to their diminutive nature, sound bars are going to be tough for you.
The small speakers in the bar necessitate offloading much midrange to the subwoofer (which hopefully will merge with the sound from the tweeter when it reaches your ears).
This may not work in a room of your size.
However, if you are dead set on a soundbar, then make sure you get something that is a plain jane stereo setup, one that does not attempt any surround sound simulation.
I think there's a polk out there that does it.
However, I would strongly advise a 2.1 system, something that's going to be more capable of filling up such a large room.
You could get a Sony receiver, Sony speakers, and Sony subwoofer for 250 bucks from Best Buy, 10" subwoofer, 5.25" speakers in the bookshelves, and plenty of power from the receiver... I think you'll find that a more capable solution in such a large space.
The alternative is a sound bar that's going to have at most 3" speakers and a 6.5" subwoofer.
I will say, that ANYTHING is going to sound better than your TV speakers, no question... I just think you'll get better sound with an actual 2.1 set up.