Not enough information about ur floor that's already their

I’m depends on if it’s a screeded floor or floorboards, both can be levelled using appropriate materials BUT WATCH FOR ....
Window and Door levels, was asked to level a floor and had to point out that if we did the patio doors which had been fitted to existing floor levels would look out of square with the new levelled floor.

Hi there, I need to know what the floor is made of ie wood or concrete also you say 45m2 but I need the dimensions.
If concrete self leveller would be suitable but timber floor is more complex and would need discussing further.
Regards Mark

If it's a concrete floor then put floor leveling compound on to get a level correct but 60mm is alot of floor to level at 45sqm but lively previous answer need more information really I would be more concerned why its 60 mm out.