Upbeat, cheerful (7)
I believe the answer is:
buoyant
This clue is a double definition.
'upbeat' is the first definition.
(thesaurus)
'cheerful' is the second definition.
(similar in meaning)
(Other definitions for buoyant that I've seen before include "Tending to float" , "Able to float" , "Lively nineteen twenties dance" , "Floatable" , "refusing to go to bed?" .)