Cushion regularly found under head of sleeper (6)
I believe the answer is:
soften
'cushion' is the definition.
(I know that cushion can be written as soften)
'regularly found under head of sleeper' is the wordplay.
'regularly' becomes 'often' (often means regularly or frequently).
'found under' means one lot of letters go next to another.
'head of' suggests taking the first letters.
The first letter of 'sleeper' is 's'.
'often' put after 's' is 'SOFTEN'.
(Other definitions for soften that I've seen before include "Make less hard or become less severe" , "Mollify" , "Make less firm" , "Yield" , "Tone down" .)