You may indeed want a rug in front of the speakers to treat the first reflection points on the floor. I would start with this and the bass traps like Agaffer mentioned. Whether you go with a single chair or couch, I'd suggest finding one without the high back. This may not be an issue if you plan to have the listening position up against the back wall. Also look for stuffed upolstry. That alone can tame alot of reflections. Start with these and then see how it sounds. You can always add what you need, but it's a pain to spend money or time on treatments and then find you don't really them after all.
