Buoyant composer reflected on complete suite, perhaps (9)
I believe the answer is:
upholster
'complete suite perhaps' is the definition.
(upholstering might complete a suite of furniture)
'buoyant composer reflected on' is the wordplay.
'buoyant' becomes 'up' (both can mean cheerful or positive).
'composer' becomes 'holst' (Gustav Holst).
'reflected' shows that the letters should be reversed in order.
'on' becomes 're' ('on' can be mean 'with reference to').
're' in reverse letter order is 'er'.
'up'+'holst'+'er'='UPHOLSTER'
(Other definitions for upholster that I've seen before include "Stuff and cover chairs etc" , "cover chair" , "Cover furniture" , "Pad" , "Pack seats" .)