Lay very softly in the hay perfectly content (5)
I believe the answer is:
happy
'perfectly content' is the definition.
'happy' can be an answer for 'content' (content can mean happy or pleased). I'm not certain of the 'perfectly' bit.
'lay very softly in the hay' is the wordplay.
'lay very' becomes 'p' (I am not sure about this - if you are sure you should believe this answer much more).
'softly' becomes 'p' (short for piano, musical term for softly).
'in' is an insertion indicator.
'p'+'p'='pp'
'pp' going within 'hay' is 'HAPPY'.
Can you help me to learn more?
(Other definitions for happy that I've seen before include "Fortunate, convenient" , "Fortunate; content" , "Doc's smiling pal" , "Blissful" , "Fortunate - joyful" .)