You cannot get a rollaway bed in all cabins and some ships do not provide them. But should you ever find any bed on any ship to not be to your liking, including sleeper sofas, simply ask your cabin steward to provide you with a 'topper'. Sometimes this will be a simple egg-crate type foam rubber topper, but other times it can be a memory foam-type topper.
47 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!