I'll get accommodation in the best possible quarters (7)
I believe the answer is:
billets
'quarters' is the definition.
('billet' can be a synonym of 'quarter')
'i'll get accommodation in the best possible' is the wordplay.
'get' indicates putting letters inside.
'accommodation in the best possible' becomes 'bets' (I can't justify this - if you can you should give a lot more credence to this answer).
'ill' inserted into 'bets' is 'BILLETS'.
Can you help me to learn more?
(Other definitions for billets that I've seen before include "Soldiers' lodgings" , "Lodgings for the military" .)