How to get 30 mm out of the floor structure?

Hello everyone,

I have the following problem: In our used single-family house, we had to remove the existing solid wood parquet during renovation because it was partially hollow (damn work). In doing so, we found the following floor structure (from bottom to top)
solid concrete basement ceiling
dry screed elements 30mm (inc. Styrofoam)
chipboard 18 mm
solid wood parquet 20 mm

I have now removed the parquet and the chipboard. This leaves me with a step of 38mm in the area where the floor is not being removed. For the new floor covering, we plan laminate with impact sound insulation and tiles in the kitchen. I expect an installation height of approx. 10-13 mm for this. That means I somehow have to compensate the missing 25 - 28 mm.

I know there are self-leveling compounds for this. For an area of about 70 sqm, I would need about 2.5 tons of this stuff. That is a) damn expensive and b) a lot of effort.

I am currently leaning towards the following solutions:
a) Lay a 22mm or 25mm OSB installation board floating on the dry screed. Edge insulation strips as a boundary and then make up the missing millimeters on the OSB board with leveling compound.
b) Completely cover the existing dry screed elements with an additional layer of dry screed elements.
c) In the hallway, slope the floor covering down to the lower level and then lay the laminate directly on the existing dry screed. Then I would have a slope in my hallway. Not nice, but rare.

Are there any other suggestions?
Which idea should I maybe reconsider?
Can I actually lay tiles on the OSB boards?
How does it behave with impact sound insulation when laying OSB boards floating?
Can I even lay the OSB boards floating, or should I screw the boards through the dry screed into the concrete?

Best regards
Andreas

Is the floor actually perfectly level? If there was something hollow underneath before, it doesn't sound like it. There is also a lightweight concrete (Thermozell), but it then has to be at least 3 cm thick. I would probably tend to also remove the dry screed elements, lay EPS-DEO boards, then 20 mm dry screed on top, and then the covering. Otherwise, the structure is not sufficient for a light and sensible solution (why twice screed elements...?), that is level and also holds. We just ripped out 65 sqm of screed, that is quite a lot of work, but you only do it once and then you can do it properly.