Self leveling as has been said

Latex self leveling compound is what you want to ask for.

It comes in a 25kg bag and you mix it with water. (If you can try and get the 2 part one, as it is better and stronger.

As has been said you will need to still float it to get a finish, but this is more just to spread it about evenly, then let the compound and gravity do its work.

Easy job. trick is to make sure the surface is totally clean before starting. And also that there are no holes where the compound will leak into.

Its normally ok to walk on the next day, but if you can leave it a good day or two then it saves damaging and scuffing it up!