Every single carriage fitted with extremely snazzy, comfy seat (4,5)
I believe the answer is:
easy chair
'comfy seat' is the definition.
(I've seen this before)
'every single carriage fitted with extremely snazzy' is the wordplay.
'every single' becomes 'each' (I've seen this in another clue).
'carriage' becomes 'air' (both can mean someone's stance or posture).
'fitted with' indicates putting letters inside.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'snazzy' with its centre removed is 'sy'.
'each'+'air'='eachair'
'eachair' going around 'sy' is 'EASY-CHAIR'.
(Other definitions for easy chair that I've seen before include "Academic sinecure" , "Item of furniture" , "source of comfort" , "It's comfortable to sit in - sounds like it" , "Comfy seat" .)