Indeed SQ's Krisflyer Gold lounges in SIN T2 and T3 are very average for a home airport. They get 1-2 stars out of 4 on LoungeBuddy. No showers or toilets. Food OK.

TG lounge is in T1 but I haven't tried it. But TG *G/J lounges are generally rather average too (even in BKK).

Airside transfers are possible if you want to try more than one lounge, but hardly worth it.

Of course there is the airside pool in T1 if you feel like an outdoor swim.