we’ve just sorted this problem – our neighbour is a musician and mostly does drum practice for 2 to 3 hour stints at all times of the day and night and the changes we made have almost entirely stopped noise through the party wall.
We used 2 layers of overlapping Gyproc soundbloc on 1″ battens – soundbloc is a heavier denser form of plasterboard.
We got it plastered so we could paint it but potentially depending on your room you could just wallpaper / line the soundbloc and paint over that.
Cost wise it’s pretty reasonable and potentially something you can you do yourself if you are DIY capable – two things to watch out for though:
1. The need to move any wall lights / plugs / radiators and re-install on the new wall. This may require existing wiring to be extended.
2. The run of your floorboards – depending on where your pipework runs and the direction of joists you may have an issue raising the outer floorboards in the future if the need arises.
It’s also worth shoving rockwool up against the party wall at floor / ceiling level in the voids between joists.