Which subwoofer?

I have a small room (10’x14’) and am wondering if a subwoofer would help. If so, which one?

I have Martin Logan electrostatic speakers with  8” powered 200 watt woofers and 8” passive radiators.  The bass is articulate, but not very deep. I am wondering if I could get more bass volume and depth without loosing detail with an additional subwoofer?
I have tried an 8” Velodyne, but could never integrate it with the Martin Logans so I sold it. 

The Martin Logans are powered by a 200 watt McIntosh receiver. 
Any thoughts?

I second this. I have a pair of ML BalanceForce 210, a bit smaller than the 212, sounds fantastic with my Wilson Audio Yvette’s.
I have a pair of rel Ti7s with my Maggie 1.7is & they integrate seamlessly. Very fast & keep up the planer's speed. Never tried them with MLs, though. They make a world of difference in my system.
Like you I'm working with a small room 13'x11, which is less than ideal.  But I'm getting favorable results using 2 Bowers & Wilkins ASW608 8" subs.

I think this topic has been discussed in great detail on previous posts, but I'm suggesting at least 2 subs as minimum for 2 channel. My mains are Dynaudio Contour 20's which on their own have significant bass response.  The B&Ws just fill in the lower end, and as also discussed previously they are set up so you don't notice them. The effect on music  is just fuller and more realistic sound.

I have them positioned in front of the Dynaudio's and facing backwards; this was based on a suggestion from JS of Get Better Sound, and it really works for the small room!

I have a pair of REL T7is with my Maggie 1.7is & they’re incredible. They’re very fast & integrate seamlessly with the speed of the planers. I also ha a T5i with my Vandersteen 1Cs & it works perfectly with them as well. FYI...I think the T5i has just been discontinued & replaced with a more expensive T5x model. Upscale Audio has the T5i closeout on sale now for $549.  I’ve not heard REL subs with ML speakers.