A few tips on SQ21:
Check-in begins at 18:30 for the 23:00 departure.
There are no showers in the SAS lounge. I managed to use one in the United Business Lounge in terminal C.
SQ have a hot food buffet offer in the SAS lounge, starting 21:30.
No pyjamas are offered as it's all J not F. I took my own.
The window seats have quite a bit more leg room than the centre seats.
Some seats are much noisier than others - avoid seats near exit doors.