Originally Posted by
tentseller
Yes, all terminal are connected airside.
T1-T3 are connected airside (walkable/skytrain). T4 is also connected airside to T2 via bus.
depending on your airlines, you may be able to check bags through at cambodia, or use the changi airside transit desks to arrange for transfer/boarding passes
there are only 3 "true" transit hotels (rates listed)
Airport Attractions - Singapore Changi Airport
the other lounges may offer access and private rooms that you can book:
https://www.loungebuddy.com/SIN
the land-side crowne plaza airport hotel has good reviews, but can be pricey ($200+)