I'm having a hard time finding any details on how the junction of IWI should look with a solid floor (tiled over stone). I've found diagrams for windows and suspended floors but nothing on solid floors.

Any help would be much appreciated.

I read it as if the floor is uninsulated. Is that correct? If, as djh surmises, there is floor insulation then yeas, as he says, dig out the floor till you get the insulation and join the 2 together. That is far easier written than done(!) and don't forget continuity of membranes.

Sorry, I did understand that the floor is uninsulated. I just stated the approved technique for dealing with an uninsulated solid floor - namely dig it up and insulate it!

Make the insulation continuous from the wall to the floor, no gap between wall insulation and PIR upstands, otherwise there's a cold bridge which attracts condensation.

If the floor were not yet insulated (in geuben's case) then just carry the insulation right down to the existing floor, and address the junction as/when the floor gets insulated. EG you might subsequently decide to dig out the floor and re-lay it, or to board over it, you can't fix the detail until you know which.

Some of the insulation mfrs have details on their websites, think I saw some on Kingspan's.

No don't leave a gap. And it's a good idea to make sure the wall to floor junction is airtight with one of the latex paints (blowerproof, aerosana etc) or I've find orcon-F works pretty well if you have a crack. The slab often cracks away for the wall and it is quite likely to be leaking air.