How would you have done it??

[ryyti]

have a house built in 1939😁 Currently renovating the basement. There is a level difference in the floors of about 120mm. (old garage)
I want to raise the level of that floor to match the rest of the house.

I’m open to suggestions / opinions / experiences.

I'm considering:
eps cement 120mm 21m² = expensive
Raising the level with gravel or alternatively Leca and pouring about 50mm of concrete??

Has anyone done something similar and can provide input?