I've flown SK on that segment you mention.

The planes are modern Airbus 340 aircraft, which i personally find much better than the B747, 777, etc.

The audio/entertainment system is superb with a large variety of english language music and shows (unlike some of the german language carriers - ie Austrian, Lauda, Lufthansa). The screens are touch which is much easier to maneouvre than those in the boeings. The audio sound system is very crisp as well.

The toilets on the A340 have windows! - very neat.

The seats are very ergonomic and comfortable. Not too cushiony which made the flight that bit more comfortable. The planes are well kept. The food is superb, the best i've seen yet (for photos of the food on the BKK-SIN segment, see http://www.airlinemeals.net for a photo i took on that flight). French wine, very nice bread, and a big, filling meal.

I would strongly suggest you get to the airport early if you are heading to CPH and try and secure seat 31H which is the exit row seat with plenty of leg room. They are usually very nice out of SIN if you check in early. I believe their early checkin is at Counter 2 at Terminal 1. You could perhaps get there around 11am to secure a nice seat for the flight later that day and enjoy the Thai lounge and explore the airport whilst you are there.

If you don't think you could do that, and you don't want to fly business, i'd strongly suggest you buy an economy extra seat, just a little bit more but better leg room.

Enjoy your flight.