The man's accompanying Welsh woman? That's the stuff! (7)
I believe the answer is:
hessian
'the stuff' is the definition.
(type of fabric)
'the man's accompanying welsh woman?' is the wordplay.
'the man's' becomes 'he's' (he refers to a man).
'accompanying' is a charade indicator (letters next to each other).
'welsh woman?' becomes 'sian' (common Welsh name).
'hes'+'sian'='HESSIAN'
'that's' is the link.
(Other definitions for hessian that I've seen before include "Coarse fabric used in sacks" , "Cloth for sacking" , "Cloth made from jute" , "Coarse jute fabric" , "sackcloth?" .)