When it comes to sleeping arrangements most types of nomadic home take the same approach. They all tend to try to accommodate as many people as is physically possible. The usual way to do this is by making every horizontal surface into a convertible bed. This works for fishing trips or taking the family on holiday two weeks per year and makes sense for that purpose. To the full time nomad, however, making up a bed every night and packing it away every morning is just an inconvenient routine that shouldn’t have to be put up with. That’s why I believe having a dedicated bed, that is permanently set up as a bed is the biggest priority when putting together a nomadic home.
For guests, it is fine to retain the use of converting surfaces for beds (usually settee seats). Full time nomads will not want to encourage overnight guests anyway. You will generally enjoy guests company for a meal and an evening, but will want to send them home or to a motel at the end of the evening, unless they have had to much to drink. The fact of the matter is that when you live a permanent nomadic life, you develop very specific routines to manage daily life in your nomadic home, which by it’s very nature, is a small space and guests disrupt your routines without even realizing it.
Most amenities share the same desirable characteristics in pretty much all of the different types of nomadic home, whether it be a yacht, motorhome, launch, bus etc.. The bed, though, is different in that respect. If your nomadic home is an RV, house truck etc.. I would want a full size bed. Probably a standard queen size 60X80 inch (1520X2030mm).
In a sea going boat and particularly a yacht, big is definitely not better. In fact it can be down right dangerous as you can be thrown around in a big bed. You will still want to retain full length in a berth but the width should be restrained to about 48-52 inches (1220-1320mm) for a double and should be split down the middle to allow for lee cloths, to restrain the occupants in heavy seas or when sailing heeled, if it is to be used as a sea berth, rather than at anchor or dock.