It is very comfy and the actual mattress keeps you warm, even if you are not using a blanket.
We have had a King-size firm mattress for a few years now, and struggle to sleep on anything else. So when our little one was ready to move into a big bed it was a no-brainer to get a King-Single Sleeping Duck for her too. Needless to say her elder siblings are very jealous, and she sleeps like a log.
Bought this mattress for our growing teenager. He's never been more comfortable and the king size single gives him plenty of scope for growth.