If there are no other options and you don't need a shower (not sure if Louis Tavern offers that with lounge use anyway, ie without a room booking), the bathrooms in the terminal are not too bad. Not up to most at Changi, but not bad. I often use the one in the baggage hall after immigration. A quieter one is on the landside, one level up from arrivals, near the far end of the terminal (past the landside restaurants).