In any event, I did not know your budget but Google (or whatever search engine) for wall mounted sound baffles. Some are much more effective even in a thin profile than most sound drywall products like quietrock. There are different configurations for different purposes that will fit in the space you have.
I'm not sure what baffles you are referring to that actually block sound transmission or isolate walls from vibration, but you have to be careful that you are using something that doesn't just absorb sound, because this will do nothing for you in this application.
Green Glue will help reduce how much airborne sound you hear coming through the wall- there is also a comparable damping compound called Quiet Glue Pro
from Quiet Rock that offers slightly higher STC, or soundproofing ratings and actually tends to be a little cheaper. If you want to reduce footfall or 'dropping things' noise you need to look for products with IIC ratings like floor underlayments.