i know it sounds barmy, but i'm a gret beleiver in Futon matresses... Not cheap crappy fake foam-filled ones, but proper ones filled with multiple layers of cotton wadding... hang em up on walls with hooks and sewn-on cotton loops at 12" intervals to make cheap absorber panels. Roll double-sized futons up into sausages and strap them in a sausage shape with a few bungee straps to stop them unrolling, and then place the rolled-up 'sausages' in room corners standing verticaly etc.
plus you get plenty of 'crashing' beds for musician sleep-overs if you just unhook them from the walls - buy cheap s/h in the free ads and they are VERY cost effective
