Subwoofer for music only ?

glad OP’s sub sounds good, most of my yap is about larger spaces, not partially filled with a bed.

rear surround, Sub(s) for Video is a different matter.

earlier I wrote "Black Hawk Down ,,,,, Room filling Impact, not directional unless you have a large Home Theater, then, a pair!".

You don't necessarily want the lows from the front for video, IF the content wants the fundamental impact coming from the rear or side.

Black Hawk helicopters, Dinosaur: coming from behind, over there ... are a great way to demonstrate the advantage of 5.1 surround’s REAR speakers. And, where's the sub, i.e. where does the director want the fundamentals of that Dinosaur Stomp to come from?

I don't know anything about large Home Theaters, 

I have only 1 sub in my small home theater, and it is adjacent to me, under the end table, facing forward. It takes some diddling with to get the crossover and volume 'right'. It, combines with the directionality produced by the rear surround speakers. My fronts have 12", so I only want 'big' stuff from my sub, otherwise, don't want much out of it. 

Many people set their rear speaker’s (and sub(s) volume too high. Normally, you should not be aware of them, but if you turn them off, the sound/image collapses to the front.

Happily existing without calling themselves out, until they perform their real purpose which is rear/side directionality and big impact.

Pseudo Surround can be worse than front 2 channel Stereo. i.e. watching "The Voice" singing contest. Donna and I often say to ourselves "they must be hearing things we are not" because that was not superior in any way. Change your AVR to Direct, or 2 Channel, it is surprising how much better it sounds. Try this for other content, often, if the original is not recorded in surround, it sounds far better in 2 channel.

When it’s good it’s good! A terrific sounding (and visuals) DVD, one of the very first:

James Taylor at the Beacon, 1998

We were there, it was an awesome concert and the DVD captures it!

"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.