sorry, not in the UK so not sure what products are there or code there.

But to add to the two others. If you can afford to lose some space, build a wall in front of the existing one and insulate with sound dampening insulation. and use two sheets of sheetrock. Also don't forget about the ceiling and floor cavity between the two places, sound will pass where it can, so making a great job on the wall and leaving it like an open window in the floor or ceiling won't solve the issue.