Just to expand on that books about books thing, here are examples of stuff I already own that fits the genre:
The Child That Books Built by Francis Spufford
How To Be A Heroine by Samantha Ellis
Among Others by Jo Walton
Books by Charlie Hill
The Book Thief by Marcus Zusak
The Shadow Of The Wind by Carlos Ruis Zafon
The Unwritten by Peter Gross & Mike Carey
Other categories of stuff I am reliably into are popular non fiction on odd topics like Salt by Mike Kurlansky or Stiff by Mary Roach; books about heists, con-artists and prison breaks like Bringing Down The House by Ben Mezrich or Papillon by Henri Charriere and anything which caters to my current fascination with magicians or my lifelong love of bodyswap stories.
I have an Amazon wishlist here if you need more ideas.
- Happy Swapsmas!