Hubby and I have always found the beds on Carnival ships surprisingly comfortable. I say "surprisingly" because we have the twin beds pushed together to make a king-sized bed....but obviously there is that "seam/gap/crack" in the middle. I ALWAYS think its going to bother me, and I ALWAYS forget completely about it and sleep wonderfully.
Best thing about the beds on Carnival: I DON'T HAVE TO MAKE THEM UP!!!!
My last cruise on the "Jubilee" the bed was so flat that I didn't get any sleep the first night then I had my room stewart bring in another mattress to top the flat one...so I was sleeping on two mattress's! I finally got some much needed sleep.
I don't know why; but I slept like a baby....guess because of being worn slap out from the day's activities and the gentle very slight movement of the ship. The mattresses were really firmer than we prefer. Our matresses at home are almost mush...time for new mattresses....LOL! Seriously though, we slept like babies even with the firmer mattress.