ᐅ Insulation of a Single Room in a Barn

Hello,
I want to build a small office space inside a barn by partitioning it off.
For this, I plan to construct four walls using a stud frame. So, I won’t be attaching to any existing walls.

I want to use 12mm (1/2 inch) OSB panels on both the inside and outside, with plasterboard or gypsum fiberboard additionally on the inside, and mineral wool insulation in the cavity.

Now, regarding insulation, I’m unsure about vapor barriers and how to handle them.

I know I need some kind of barrier to prevent air from passing through.
But should it be a vapor-permeable membrane or a “regular,” airtight foil?
And should the barrier be placed on the inside, outside, or both?

It’s worth mentioning that the space won’t be used daily.
It will only be heated every few days on weekends. It’s not for continuous use. So, the solution should be cost-effective and balanced in relation to the expenses. If there is a reasonably good solution that is much less complicated but works satisfactorily, that would be perfectly fine for me.

Thanks in advance