After doubling his final instalment, Del has gold furnishings (5)
I believe the answer is:
decor
'furnishings' is the definition.
(decoration of a room)
'after doubling his final instalment del has gold' is the wordplay.
I cannot quite see how this works, but
'gold' could be 'or' ('or' is the heraldic name for gold) and 'or' is found within the answer.
The remaining letters 'dec' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for decor that I've seen before include "Embellishment of a room" , "Style of furnishings, drapes etc used in a room" , "Colour scheme, furnishing etc. of a room" , "Style of furnishing etc used in room" , "stage background" .)