Use the usual Warforged Racial Modifiers for your character.
History of the Librarians
You were not made for battle, like the warforged of Eberron. Instead you were one of Librus - God of Legacy’ creations in his vast library. At some point you were found, probably inactive. Inside you still a tiny sliver of Librus’ essence. Your labor, a valuable resource was acquired by an artificers modifications. You were allowed sentience, at the cost of your labor. Yes, for a time you were a slave. Not the magnificent, all knowing, shushing librarian of before, but now, now you could think, wonder, dream.
But through the words and actions of Melter, you realized you could be your own entity. Your owners realised, maybe slowly, maybe by force, that you could not be owned.
Many librarians count their age from the day they were freed, the day they owned themselves. They might refer to negative numbers of age if questioned hard, but would rather not speak much of a time they were not free.