Small tip on the side: Fermacell gypsum fiber boards, double mounted, with insulation (Isover Akustik) in between. Advantage: they can be easily dismantled during a later renovation, are slim and easy to install - primer on top + paint, done. Alternatively, I would use an 11.5 cm KSV / KSL (solid brick, perforated brick), according to structural engineering. However, more complex to produce TW + plastered on both sides. Gypsum boards, expanded clay or bricks also work.
Regards