The best option will be the use of a sand-cement screed with a thickness of 40 millimeters or more, since only in this case you can hide all the main disadvantages and level the floor surface in order to proceed with further decoration, namely, to the further installation of the flooring. But remember that if the floor is very badly damaged and forty millimeters will not be able to hide all the shortcomings, then a slightly large thickness is selected. But in any case, remember that you do not need to use a too thick layer, because it will look inappropriate and to some extent even stupid.