The common misconception is that in small rooms the low frequencies must build up in the room to be heard. What we hear is due to compressions and rarefactions in the air. As the cone of the speaker moves back and forth it creates these variations in air pressure that then travel through the air to your ear. If the cone moves back and forth at 20 Hz then the ear hears it as 20 Hz. The ear doesn't know how far these waves of pressure travel before they arrive. You can put your ear an inch away from the woofer and hear the bass.
Yes, the dimensions of the room will play a huge part in reinforcing certain frequencies, but you don't need a big room to get bass.
I agree that small rooms can be problematic for a variety of reasons, and one with equal walls even worse, but you can still get plenty of bass. I also agree with monitors, and I would use a sub. Most big speakers require that you sit further away than this room will allow.