TK used to use Premium Plaza but it seems that they are using HX lounge.

It seems that SQ is the only *A airline lounge left, and I'd suggest that you go there first if you arrived 3+ hours before departure. Food there was very good and there were showers too. If I were you I'd go there first: 2 reasons: 1) they close before the last SQ flight out; 2) SQ lounge is located before the train to TK gate.

You will get a lounge invitation for the HX lounge and you can use your *G status to get into the SQ lounge (ask again at check-in and they will re-confirm the lounge locations).