Paying for a business class ticket only to sleep on a bench in the airport...wow.
but staying positive and supportive,
you have 2 excellent lounges (Eva and Singapore) and 6 or 7 mediocre Thai Airways lounges to access for free.
the SQ lounge is at the junction of DEFG.
This is a plan you can apply.
Dine and wine in the Singapore Lounge
sleep in the massage seats/ sleeping room in the Eva lounge
they close at night unfortunately.
kill time walking from concourse F Eva lounge all the way to concourse C Thai lounge, and then walk all the way back to concourse G for more Thai lounges.
kill more time with photos with the giant naga statue, window shopping,
plane spotting (count how many emirates A380s you can spot in one day)
and watch a movie or tv series on your laptop during 2am-6am when you are out on the benches.
16 hours will fly by!