ᐅ Poor Insulation: Vapor Retarder or Vapor Barrier in Timber Frame Construction

Hello,

I want to renovate our bathroom. Our house is timber frame construction with glass wool insulation and gypsum fiber boards (Fermacell).
My ideas are:

- Replace the glass wool with wood fiber insulation
- Use OSB boards and then gypsum fiber boards again as cladding --> more stable walls for tiling afterwards
- I am unsure whether and where to use a vapor barrier or even a vapor retarder foil between the insulation and the cladding

Is this all appropriate for a bathroom?

Regards
Alex