As all terminals at Changi are interlinked by the Monorail, you may want to know that there is a larger and more modern Transit Hotel in the impressive Terminal 3. This is where I stay every time I pass through Changi.

Regardless of which hotel you choose to stay in, you have access to the swimming pool (rent a towel), free in-room LAN internet (no wifi, though), tea-making facilities, and, unless you're in a "budget" room, you have your own toilet and shower, as well as a bed, obviously

I think you can only purchases blocks of 6 hours at the hotels, so if you are only at Changi for 4 hours, then remember that you won't be in the room for long, so perhaps may not be getting top value for your Sin Dolla.

Have you considered the Ambassador Transit Lounge? It's basic, but it is nice to rest for a few hours, with TV, internet access, food and drink, plus showers. It's cheaper than the hotel, but I don't remember the exact price, sorry.

Alternatively, why not just relax anywhere in Changi Airport? It is one of the few airports in the world that doesn't feel like an airport. It's the best airport in the world, and I presume you haven't been there before, so don't go there thinking it's like a UK/US airport, because it certainly isn't!