Reserve the transit hotel for a block that will let you get the sleep you need, for example nine hours if you want to sleep for eight hours. There is a transit hotel in each terminal, although I've only used the one in T3, which is the newest. One of the other transit hotels was recently closed for renovation, so it's had some modernization and upgrades. At least one offers budget rooms without private/ensuite toilet and shower facilities.

The T1 SkyView lounge is pretty decent and certainly is open all night, but IIRC it limits visits to several hours, although I don't know how they enforce this. There's a large and quiet area about a half level above the main area. You access it by hidden stairs at the far left wall, near the toilets and showers. I don't recall seeing any seating on while one could comfortably stretch out and recline.

I haven't seen the T2 SQ lounge since it was renovated, but the biz side of their T3 lounge impresses me as always busy at all hours. When you can book (do make an advance reservation as they get full most nights) the transit hotel for $80 or less, IMO it's not worth sleeping in the lounge and worrying about your belongings.