Buildup for patio door threshold

Hi, new to the forum.
I'm currently doing a slow renovation/refurb/retrofit on my 1930s house.
Getting the place warm and dry is my priority. I'm currently working on fixing the ventilation to the suspended sub-floor and then I'll be insulating it.

In the process I've come across this threshold for the patio door, which is currently a cold bridge as the build up is just concrete poured onto some flimsy DPC between the ends of the floorboards the door frame which is installed to the outer leaf, so that the concrete sits across the inner leaf, cavity, and part of the outer leaf (see photo). The cavity is also full of damp debris so needs to be cleared, then I'll add a cavity closer and insulate. I've come up with the attached build up which is intended to thermally decouple the masonry from the room. There is also DPM as a vapour barrier on the warm side of the insulation, which will be taped onto the door frame and hidden with flooring trim. I'll then either tape this to the top of the PIR that will go between the floor joists, or lap and tape it to a separate vapour barrier that would be laid across the joists and insulation depending on whether I use a separate barrier or just tape the edges of the PIR to the tops of the joists.

Does this look like a good approach? Anything that could be improved or simplified?
Cheers

You would expect the dpm to lap the dpc if there is one otherwise damp can come in under the sill

Thanks that makes sense. Unfortunately it looks like when the opening was originally made it went in below the level of the dpc on the outer leaf. The one on the inner leaf is there but it's the original bitumen so I can't really lap into it. Would it make sense to put some new dpc along the top of the outer leaf, below the cavity closer and then fold the new DPM down instead of up?