If you liked the anime, you can continue it from the translated web novel that continues from where the anime left off.
Also because i'm a dick, here is a spolier warning.
You know how Subaru has to deal with a lot of confusion regarding the contents of a letter being blank in the anime, causing Ram to be hostile to him when he returns.
Its blank because Rem was erased from the world's history much like the white whale by the time the letter arrived.
Shes now a vegetable who no one remembers except for Subaru, and because the save point is after this, its set in stone and he can't fix it.
The novel is really good too
Oh there are multiple witches, not just the witch of envy. Except envy kinda killed them all. Subaru does meet the shadow of the witch of knowledge though.