What door lining for a 4 x 2 CLS wall

I am about to build a CLS wall in my house and have decided to go with:

• 38mm x 89mm (4x2) timber
• 100mm thick Rockwool sound insulation
• 12.5mm Knauf Sound panel tapered edge plasterboard
• Gypsum Thistle Multi Finish Plaster.

It's not a big wall and i have read lots of useful articles including this article (The best one i have read) but this is where i'm stuck, what door lining size do i need?

I know the finished sizes are:

• Timer = 89mm
• Plasterboard = 25mm (one each side)
• PLaster = 4mm (i've read about on each side)

So with the above sizes, is the door lining i need something like 27.5mm x 120mm?

Timber and wood coming from Wickes and on the timber page, it recommends the above size but not too sure at all.