How to approach this wetroom floor...

[Workerbee]

Hello! I'm turning my tiny bathroom into a wetroom and I had a couple of questions I hoped you guys could help with. Current floor is concrete slab, with 50mm EPS then chipboard, and previously had a shower cubicle with raised tray. I'm taking it back to the slab and hope to put a wetroom shower former where the shower tray used to be, electric ufh and stone tiles. 

 

First question is about supporting a wetroom shower former and floor tiles on a floating floor.

Having done research and spoken to insulation and shower tray manufacturers, I've got a few possible solutions I want to run past the forum:

1) Phenolic/PIR insulation (preferably 75mm), then cement board (22mm?) - insulation manufacturer thought this would be fine to tile on, and would be my preferred option insulation-wise, but I'm aware tilers sometimes say tiling a truly floating floor isn't a good idea. I'm also unsure how I would then install the shower former, as I presume it couldn't just rest on insulation.

2) XPS tile backer board - maybe 90mm for most of the floor as I could do away with the chipboard. Leave a rectangle out for the shower former, and drop in 30mm XPS then 38mm screed, then place the 22mm former on top to bring it level with the rest of the XPS floor. Advantage is better compressive strength with XPS and it could be stuck to the slab, so creating a more mechanical fix between tiles and slab than a usual floating floor. Worse insulation, though.

3) Phenolic/PIR fitted between wooden joists screwed directly to slab, mimicking floor joists that the shower former could slot between. Advantage is high strength; downsides are large thermal bridges throughout the floor, and wood in a wetroom floor, where it could rot.

 

Second question is about how to deal with the current shower tray slab and drain. I've attached a few pictures.

Where the raised shower tray used to be, there is a horseshoe-shaped concrete slab on top of the concrete floor slab, that came level with the insulation and chipboard on the rest of the floor. I'm thinking I should chop this out with an angle grinder and start again from the floor slab, using one of the above floor buildups. The drain is resting on sand, as there is no slab in this part of the floor. Can I keep it like this and just connect into the existing drain?

 

Thank you for any advice.