You have a good amount of open room volume to consider, nit just the living room. This is important for getting the right sub for your situation.
Also, what's your budget?
Say, for 2500'3 - 3000'3, you could look at the 2000 or 3000 series from SVS, Hsu VTF-2... I have 2 Outlaw x-13s in a 2000'3 room.
Monolith 10 or 12" subs... Rythmik has some 12" subs that many like, though their sweet spot is the 15" variety.
Nothing wrong with "too much" sub, however, I'm a big fan of encouraging dual subs! Dual Hsu VTF-2 subs should take care of you pretty well! Great performance for the value: arguably the value leader.
http://www.hsuresearch.com/products/vtf-2mk5.html
Hope this help... Happy hunting!