Simplest; most relaxed (7)
I believe the answer is:
easiest
I believe this clue is a double definition.
'simplest' is the first definition.
(simple can mean easy or straightforward)
'most relaxed' is the second definition.
('easy' is associated in meaning with 'relaxed')
(Other definitions for easiest that I've seen before include "Most comfortable" , "most relaxed" , "Posing least difficulty" , "Simplest" , "Least difficult" .)