In the UK on a 2-month assignment from the US for my work, my wife and I have taken several weekend jaunts, but Oxford has been my favorite so far. I picked this book up at the tourist information center from a selection of dozens of different tour guides and "Walks through . . ." books. It is affordable (about 6 pounds), portable (fits in a large pocket), and maps out several walks you can take starting at the city center working outward.
The copyright date is 2010 so the information seems to be current (Harry Potter movie sites are mentioned), and it seemed accurate as we followed some of the trails through Oxford. The index seems a bit skimpy, but using the map on the insight covers and the more detailed map for each tour as keys you should be able to find what you are looking for.
FYI, for my best bet of don't-miss things to do in Oxford:
--Do an early lunch at the Eagle and Child pub, and you might be able to sit at the very table where C. S. Lewis and J. R. R. Tolkien discussed their books and ideas over ale.
--Do a tour of Exeter College. Just over the garden wall from the busy central quads of the old Bodleian Library and the Sheldonian Theatre, it is a world apart of quiet green gardens and comfortably warm and worn buildings that inspired Tolkien as a student.