Soundproofing garden room office

Hi,

We have a garden room office that is around 110mm from the garden fence we share with neighbour. The garden room has 100mm rock wool, plasterboard and skim on inside. Outside it's OSB boards (or concrete boards not sure) and Cedar wood.

Immediately on the other side, the neighbours have a trampoline - so kids being kids shout and scream a lot.

So thinking of some sound attenuation ideas.

Exterior:

• Build a small modular exterior type plywood box. Plywood 12mm thick. Two sheets. On the inside put mass loaded vinyl and / or high density plasterboard and then some rockwool. This would be 1200mm high so you stack one sandwich box on top of the other in the 110 mm gap between garden room wall and fence. Total height 2.4 M. The density of the plywood and the MLV + chipboard on inside of plywood box would give you some sound attenuation. It's difficult to get into that tight space to put pillars in to support the boxes - so instead they would slide in.

Interior (advanced):

• Put in a second layer of high density plaster board on interior over existing with a layer of MLV in between. Then reskim. I'd loose probably 50 mm in width and length of room. I am ok with that. Now, this would be above my skill level, so I wondering who could I get to do this?

Interior (simple)

• You can get some sound absorbing (not proofing) tiles. These ones have some MLV, so you get a little bit of proofing also https://www.amazon.ie/dp/B0FXW56G8K/?coliid=I328BA9XLOIF04&colid=2TEQNI8AZ99H2&ref_=list_c_wl_lv_ov_lig_dp_it&th=1

Not point me doing simple if I could get someone to do the advanced interior option. How much do people think it would cost, room size is: 1800mm width and 3300mm length.

Note: I am not looking for 100% sound proof - just to muffle sound

Note 2: I don't want to get into the politics here. Obviously kids have a right to play and shout and obviously the neighbours might move it at some point. That's all moot, I am trying to just figure out options.

Thanks