A forum post by CD Projekt Red's Marcin Momot gives some additional details as to the working of The Witcher 3's upcoming and much requested New Games+ mode.
New Games+ is the final free DLC for The Witcher 3—due for release at an unspecified point in the future. Momont's post clarifies what will and will not be carried across for players embarking on their second playthrough.
The player's experience points will be transferred across, although players below level 30 will bumped to that level on started NG+. Items will also make the jump, but not quest items, books, letters, usable items, trophies or—tragically—Gwent cards. Money and alchemy recipes will be carried across.
When you start NG+, Momot reveals, you'll be able to select any difficulty level. You'll also be able to obtain the Death March achievement in NG+ mode.