Water beds are just that - beds filled with water! There are two types of water bed, soft sided water bed or hard sided water bed. The more expensive water beds are made to lessen the wave effect which was common in the early models. Water beds are usually heated and a thermostat controls the temperature.
It is always important to make sure that you receive a design visit from a bedroom designer beforehand. When they turn up they should be professionally dressed and be asking the right questions. During the design visit they should be measuring up the room in detail including the ceiling height. This visit should be free.