Subwoofer for music only ?

"Thus, my preference, IF subs, use a front facing stereo matched pair, located adjacent to your primary speakers. "

I would stay away from this type of installation, unless your value aesthetics over getting the best sound quality.

We position our main speakers to provide the best best overall sound, but their ultimate position does not guarantee that the woofers are in the optimum position for low end accuracy. Adding a pair of subwoofers will only address room deficiencies if they are placed with that in mind.

Keep in mind that whatever problems with the woofer positioning, will only be exacerbated by adding more low frequency energy to that same location.

For purposes of 2.0 stereo, you cannot do better than REL. GO TO THEIR WEBSITE AND THEY HAVE A TOOL THAT WILL HELP YOU SELECT THE PERFECT SUB FOR YOUR ROOM BASED ON YOUR ROOM SIZE AND SPEAKERS  

Whatever you choose, try to avoid convention and go nearfield. By dumping all the energy into your listening seat, you avoid problems with room boundaries. You owe it to yourself to try this.

That's a small room.

How do you posture yourself to listen to music?  Do you sit on a chair between the speakers?  Do you sit at a desk?  Do you lie on the bed?

For the best listening experience in a small room like that I would first get rid of the bed.  If that is not possible, then you could probably sit on the edge of the bed, pull your speakers several feet from the wall, and move your sub around until it sounds good.  If you have two subs it will be easier.

I use a single REL T/5x in 16' x 22' room and it sounds great with a pair of Harbeth P3 ESR speakers.  Plenty of bass for me.  If you are a huge bass hound and play a lot of EDM and hip-hop at high volume, I'd shoot for a T/7x in that tiny room.  There are other subs, but for my room, speakers, and listening habits the REL t/5x is perfect.  YMMV.

Will your wife be in the bed with you? She could adversely affect the listening experience, or possible enhance it depending on the resonance of the room.