Soundproofing of an apartment wall in an old building

Hello everyone,

I want to insulate the wall to the neighbor's apartment in my bedroom against airborne noise coming from there.
It is an area of about 12sqm, with a wooden floor and stucco on the ceiling.

I have already done some research and I think it will come down to something like a secondary wall with 50mm profiles, mineral wool, Kn*** diamond boards, etc... my question is:
Who should I contact? A drywall specialist? I want to make sure that the measures are effective and that I won’t regret later if the work is done neatly but, for example, the wrong system is chosen for my case.
Should I contact a building acoustics expert first?
My fear is that it might be someone who claims to be knowledgeable but ultimately only wants to fill their order books – if you know what I mean? Now I still have all options open and want to make sure the best possible method and implementation is chosen.
Thank you!

Measure with risk! The project can bring an improvement but does not have to. What is important is how/where the sound is transmitted. It can be through the wall or also through the floor slab. It can also be both. If it happens, for example, through the floor slab, the wall insulation can almost be in vain. However, it may also be that the insulation of the wall achieves the desired effect. I would initially consult a freelance expert who can provide advice. The costs will certainly be lower at first and then you can see further. Unfortunately, I don’t know if there are options to measure where the sound is coming from, but all in all, it is probably better than just acting blindly.

Google "soundproofing mats engine compartment." You will then be shown those things used in shipbuilding. If you attach them to the wall and cover it with drywall, it's quiet. Really. Aixfoam for example. Karsten