y wife and I have decided to finish the wall in our bathroom with T&G.
I have pointed out to the better half that T&G and water don't mix
pointing out that the strips will expand and contract creating cracks
between the strips - I lost.

So I was wondering if MDF grooved to look like T&G and primed with
PVA, then painted would be a better option.

I have already screwed batons to the walls ready for the T&G strips,
but I'm not sure I still need them with MDF. I'd rather keep the
batons as I don't like the idea of gluing the MDF directly to the
wall, moisture is bound to get in and stay there. Also I've planned
all the bathroom dimensions with the batons in place.

Also does anyone know which large DIY stores sell MDF matching? It
has to be at least 2.1m high and ideally 2.4m wide. Smaller width I
can live with.

Thanks in advance,
Martin