Bob and I totally disagree on this, he comes from a HT perspective while I am oriented toward audio. There are several subs that will work, I use REL and Hsu. The larger subs will overpower your room, I have a pair that use 4 12" a side in a large cabinet and I don't use them in my room which is similar to yours except being twice as long. Two 10" subs will give you all the bass you need in a room your size. Or one 10" or 12" if they are good quality. I would start with one better one and add a second later rather than start with 2 cheaper ones if that was the choice. There are several other powered subs that I have not used that have good reputations.
