Bringer of good luck in old lady's bed (6)
I believe the answer is:
mascot
'bringer of good luck' is the definition.
(I've seen this before)
'old lady's bed' is the wordplay.
'old lady's' becomes 'ma's' (both can mean mother).
'bed' becomes 'cot' (cot is a type of bed).
'mas'+'cot'='MASCOT'
'in' acts as a link.
(Other definitions for mascot that I've seen before include "Lucky charm" , "Thing believed to bring good luck, perhaps to team" , "Thing believed to bring good luck to, say, team" , "One for good luck" , "Character or object used to bring good luck, or represent an organisation" .)