Elated ( Informal ) (2,5,4)
I think it could be either:
on cloud nine
(Other definitions for walking on air that I've seen before include "Highly elated" , "Extremely happy" , "In seventh heaven" .)
(Other definitions for on cloud nine that I've seen before include "Ecstatic" , "Elated" , "Transported" , "Extremely happy" , "delighted" .)