Monitors or floor speakers for small room?

Marakanetz is correct. You only have to pick the sound you like. Sub/Sat gives you the freedom to place the bass exactly where you want it and place the mid/tweet where they image the best. This assumes a very high quality sub and careful crossover. The floor standing speaker for your room should work well with it 3-5 feet into the room and your sitting position 9-12 feet away. This is what I prefer. My room is 17' wide and 25' long but there is a grand piano and assorted things behind the listening position. It puts me half way back in the room so there is no problem with reflections off the back. It is a little like sitting 15 rows back in the concert hall. I have floor standers for 2 channel and cross over at 80 Hz with the subs for SACD and Blu-ray. Your room could be used this way if you like. Good luck and be sure to have fun!

Since you already own monitors...the next logical step would be to add a sub...that being said...I recently went back to full range floorstanders and have been happy with the results...I could never achieve that big sound with monitors...even with a sub...

Smaller rooms with reflective surfaces can benefit from a system using waveguide loaded tweeters. The waveguide evens out the power response, so that reflected sound will tend to carry the same relative balance across the critical midrange and highs.

Floor standing 3-ways with small mids (less than 5") that cross around 2500Hz to a capable tweeter may also provide that smoother off axis response.

Of course, your options open up if you're willing to add a few absorbing panels between and behind the speakers and at the first reflection points. That definitely cleans up the sound stage and imaging.