Has anyone added a small subwoofer to 2 channel and been thrilled with the result?

The subwoofer can of worms.
I’d like to add some bass to my otherwise fine 2 speaker setup and have limited space so perhaps a single 10in?
After a few weeks of research the only conclusion I can come up with is - everyone agrees they have to be setup properly. Every brand and technology has their own following and most recommend using 2 (which I don’t want due to space concerns). My room is 12 x 13 ft with box raised ceiling.
After much research, these are the subwoofers I’m trying to pick from, for various reasons:
Rythmik FM8  - lots of hifi fans
JL audio e110 - fantastic support
REL T/9i - sort of a gold standard
KEF R400b - interesting technology, makes me grin. 

I've never heard any of these.
Hegel H160
SF Concerto speakers on stands.
+1 on REL. The best decision I made was to add a REL T5i sub to my system (room size 12x16 feet). I was on the verge of upgrading my Dynaudio Contour 20 bookies to the bigger Contour 30 floorstanders due to a slight lack of bass (noticeable with jazz and electronica). I realized upon auditioning the Contour 30’s that I preferred the imaging of the smaller Contour 20’s and adding a sub would be a more affordable option as well. Turned out to be the best decision as the C30’s would have been overkill due to my room size. Once I got the REL dialed in it brought my system to another level. Hope this helps! 
@lance-baker The op stated he wants to 'add' bass to his 2 channel system, not win a SPL competition. DVC setups are unnecessary for what the op is looking for. The op also stated his room is 12'x13' so it's not going to take much to add some additional 'weight' to the sound in that size room.
I have a 2nd system in a smallish room (10x18) with WharfeDale Denton 80th's (5 inch drivers).

Space and aesthetics were constraints for adding a sub in this room, but I ended up buying a small sealed sub by Cambridge Audio - the Minx X301 (8").

Like others here, the small sub really helped improve the sound.  I'm not a base-head - just needed a more weight, and the little Minx did that.

I had two Minx subs in this system for a short while and that was indeed better.  I have a MiniDSP and will probably play with that in this system at some point.

It may take a few passes – or even a few days – to get things just right. You might even upset a few neighbors or roommates along the way. But that glorious moment when your subwoofer is delivering the kind of bass that makes your spine tingle is worth any associated work and grief. Have fun! => https://goo.gl/VgHZ6R