ᐅ What type of screed is suitable for loose sand with stones?

My floor in the newly purchased old house consists of stones and sand. What should I put on top to get a solid, level floor? Only wooden floorboards will be installed on the surface, so it won’t be subject to heavy loads. Also, I have to carry everything up a hill with a 50-meter (164 feet) elevation gain, so I am trying to avoid using unnecessary amounts of material. I am thinking of about 2 cm (0.8 inches) thickness. Should I use concrete, self-leveling screed, or what would be recommended?

Do not use screed; instead, install battens for the floorboards – just as was traditionally done.