This is quite a technical question, sorry I am not expert in  this field, cheers.

It's not easy to do a 100% sound proofing room and it will be expensive to do so also.

Maybe you can approach sound proofing suppliers for solutions as there are many products in the markets from noice reduction foam pad, acoustic panel, double wall construction with acoustic mineral wool, the use of sound absorbing materials for wall, floor, ceiling and furniture, sound proofing blanket, even special painting works, etc.

Yet, if there is a hole leakage at windows and doors which highly likely, it will spoil all the good sound proofing works you did anyway. So you will need to seal all the windows and doors properly.