We slept on a Murphy bed that converted to a sofa at the Kauai Marriott. The bed had a regular Marriott mattress and was very comfy. Imagine the look on my face when we walked into the room and instead of the promised queen bed we saw only a sofa - I was going to march down to the office and have a nice talk with them. Fortunately, we quickly realized that the wall of shelves above the sofa could be lowered down… Voila, and there we had a nice bed!
Just one more thing… Murphy beds are NOT cheap. Here are some prices of the ones sold by Costco: