You're thinking "oh nuts, I have a sound problem"; we're thinking "oh cool, we get to work on vertical room modes not just the horizontal ones"
First, I would DEFINITELY try putting the sub against the back wall behind the blue couch. The impact on sound will probably be much less than you think.
Second, I couldn't find room dimensions anywhere in the thread; any chance you could provide approximate length width and (most importantly) height ?
Worst case, you could probably combine some bass trapping with headrests for people in the upper couch and kill two birds with one stone
