get about 6 mattress coverall the walls in your room it muffles the sound thats what i did with my band back in the old days,it will get really hot though
what is polystyrene going to do? If youre going to the trouble of sound proofing your room, you might as well do it right and spend a couple of grand...but there is an easier solution, theyre called headphones, you could get some for like $30