I sleep with nothing on, like Snow White (7)
I believe the answer is:
fairest
'like snow white' is the definition.
(I've seen this in another clue)
'i sleep with nothing' is the wordplay.
'sleep' becomes 'rest' (synonyms).
'with' is a charade indicator (letters next to each other).
'nothing' becomes 'FA' (slang term - sweet Fanny Adams).
'i'+'rest'='irest'
'irest' put after 'fa' is 'FAIREST'.
'on' acts as a link.
(Other definitions for fairest that I've seen before include "Very lovely" , "Most beautiful" , "'''Mirror, mirror on the wall, who is the ... of them all'' (Snow White's stepmother) (7)'" .)