The sounds you hear from next door depends on many factors, (some of which you can control):
The reverberance of your next door neighbours house or rooms within house ie do they have carpets, fabrics, loads of furniture to absorb the sound?
The transmission through the party wall - mass of a wall is important to reflect the sound energy back. So double brick thichness walls, heavily plastered is generally best. As suggested in previous comments, make sure the wall does not have holes, gaps in plaster etc in bedroom and above bedroom in loft area.
Chimney stacks are a problem as the seperation in often only one brick thick at times. Block up the chimney if not in use but consider other implications of doing this.
Also check that the sound isnt simply coming to you via their and your open windows.
The reverberance of your room receiving the sound. Again loads of furniture, fitted wardrobes on the party wall, carpets, fabric and stuff to attenuate the sound in your room is good.
The level and frequency of sound. I think low frequency sound goes thru walls quite well. Not a lot you can do with a heavy snorer.
The level of background noise at night. At night, noise if of particular concern because background noise is low. If its really a problem, you can introduce a low-level background noise in your house via say a speaker in your loft (its called acoustic perfume!) so that you won't notice other sounds at night. Dont know of any makes but would be simply switched on and would emit a continuous broad spectrum sound that you wouldn't notice after a while.
Anyway, those are the main considerations. I do know that special acoustic materials are expensive and quite often don't work properly. The reason being that a heavy wall is best to reflect the sound back rather than special materials to absorb the sound as it comes through the wall.
Only other thing to suggest is sleeping pills and ear plugs!
Hope this helps