I enjoy doing altered books too, and enjoyed ur weblink to yours very much.
See photo below...I made this little book with envelopes. So cute and easy. Just seal the 9 x 12 envie, but off the ends (barely), fold over 1/3 then glue them together back to back using open ends for tags etc. Cover all the open spaces with paper and ephemera and make a fold down section and glue into book.
I love to decorate envelopes!