I actually mentioned Einstein's Unified field theory. I think the Unified theory you're thinking of is a "theory of everything" and closely related to unified field theory, but differs by not requiring the basis of nature to be fields.
Here's a link to a book that might answer your questions. Its expensive!
Also "Conversations with Einstein." By A. Moszkowski is worth reading if you like Einstein.
In a recent post you mentioned Einstein's unified theory. I know he worked on that but was not aware that he ever published such.
Could you point me toward such publication?