Favourite one in Paris, one with a bloomer (7)
I believe the answer is:
petunia
'bloomer' is the definition.
(petunia is a kind of flowering plant)
'favourite one in paris one with a' is the wordplay.
'favourite' becomes 'pet' ('pet' can be a synonym of 'favourite').
'one in paris' becomes 'un'.
'one' becomes 'i' (Roman numeral).
'with' means one lot of letters go next to another.
'pet'+'un'+'i'+'a'='PETUNIA'
(Other definitions for petunia that I've seen before include "Common garden plant" , "Popular plant for baskets" , "Plant cultivated for its white, pink, blue or purple funnel-shaped flowers" , "Garden plant with large funnel-shaped flower" , "Auntie foolishly made under pressure" .)