Big party on a bed warmer (5)

I believe the answer is:

doona

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'bed warmer' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'big party on a' is the wordplay.
'big party' becomes 'do' (do is a kind of party. I am not sure about the 'big' bit.).
'do'+'on'+'a'='DOONA'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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