Express perhaps support for book (9)
I believe the answer is:
paperback
'book' is the definition.
(I know that paperback is a type of softcover)
'express perhaps support for' is the wordplay.
'express' becomes 'paper' (the Daily Express is a newspaper).
'perhaps' becomes 'back' (I've seen this in other clues).
'support for' means one lot of letters go next to another (in a down clue, some letters 'support' others).
'paper'+'back'='PAPERBACK'
(Other definitions for paperback that I've seen before include "Book with soft cover" , "Publication" .)