If you are leaving from Terminal 4, none of Changi's hotels are in the building. The transit hotels are at T1, T2 and T3, and Crowne Plaza and YOTELAIR are in the public area beside T3 and in Jewel.
What it means
Plan the shuttle as part of the trip. The public shuttle takes about 10 minutes and runs 6am to midnight, then as a loop about every 19 minutes. The transit shuttle takes about 12 to 19 minutes, and you need a through-checked itinerary. Add security at the other end.
See our short lists for T4 for the stays we would pick.