A new mod for The Witcher 3 called the Enhanced Edition will allow players an added difficulty should they desire it.
The Enhanced Edition mod alters the default stats and abilities of the game as well as a variety of other things like meditation, alchemy settings, and equipment durability.
Included as well is a 'Hardcore Enemies' setting, lifting enemies 11 levels above the player, the combat is also made tougher by altering the combat and damage systems.
The full list of changes can be seen on the mod's official page.