Waterproofing plasterboard bathroom walls - Membrane OR Jackoboard + Membrane

Ikeepgettingfines

Hi,

I am currently getting my bathroom refurbished. The walls and floor were stripped completely.

Due to having a solid brick wall which meant that the internal walls were very cold in Winter, I decided to put 37.5mm thermal plasterboard on the brick walls.

Now, I need to waterproof the walls, especially the one around the bathtub.

I am thinking:

6mm Jackoboard glued with Jackoboard Board Fix Adhesive on the thermal plasterboard. And then use Mapei Showerproofing kit (membrane) all across the bath tub on the Jackoboard. And then finally, porcelain tile will be glued onto the Jackoboard with cement base flexible adhesive.

I understand this will add an extra 6mm on the current 37.5mm thermal plasterboard + tiles + membrane + adhesive. But I want to make sure this is the right way forward?

Or do I just go with the following plan:

37.5mm Thermal Plasterboard, then Mapei Showerproofit Kit membrane + Tiles glued with rapid set tile adhesive?

The whole bathroom floor is being done as such: Joists, then moisture resistant chipboard, then NoMorePly 10mm XPS Backerboard, then Mapei Showerproofit membrane, then Ditramat, then Tile adhesive and then tiles.

Thank you for all your advice.