Suspended to solid uneven floor advice

[GasManDan]

After a bit of advice if poss please folks; 

currently undergoing a complete downstairs remodel before we start the rear extension. We have cut in a new doorway into what will be the utility and downstairs bathroom. 
In the new utility I have had to break through the concrete slab to pick up & tee into the soil stack. I’ve back filled the holes today in prep to fill back up with cement. The floor in this room Is approx 40mm out in the middle so was planning to put some self levelling screed down. The now hallway that leads into the utility is suspended floor that is pretty much flush with the concrete slab. As I’m planning to put underfloor throughout the downstairs (seen that omnie do quite a good design) by the time I’ve replaced the suspended floor boards with the t&g back boards and then the uf on top of the existing solid floor and screeded+floor covering, there is going to be a massive difference with height and this is what I’m trying to avoid! Any help or advice would be appreciated thanks 

[Mr Punter]

What is your question?  If you want flush floor throughout you will need to build up the lower floor.  You can lose a bit of change of level via a threshold at or near a door.

[GasManDan]

10 hours ago, Mr Punter said:

What is your question?  If you want flush floor throughout you will need to build up the lower floor.  You can lose a bit of change of level via a threshold at or near a door.

Sorry I’m not that clear at times! 
yes basically, I want a flush floor throughout the downstairs but I guess the thing that is dictating this is the amount I will need to raise the solid floor in order to make it level!? 
To add another problem to the mix is that I want to install an UF heating system that will work with a combination of both an existing solid and suspended floor that are currently at the same level?