Looking at fixed beds you have three basic layouts, side bed, transverse bed and rear with central toilet.
Side beds come in two different formats with either the bed tucked at the back corner with a toilet compartment alongside or with a toilet across the back and the bed ahead. The first option keeps the length and weight down but the toilet will be cramped. The second gives more room for dressing, washing etc and can still keep length down. The main drawback is the fact that one person gets the outside and if the other needs the toilet in the night they have to climb over the first one.
The transverse bed is across the caravan, it does allow you to get out both sides and is easier to make up but once down it does restrict the room at the foot making it difficult to pass an many models. If you look at this check you are happy with this although the bed will slide back during the day making the passage normal.
The centre toilet and end bed possibly needs the most length but gives you a separate bedroom cut off from the lounge and is best if you are likely to have others with you as it gives far more privacy at night but the smaller dimensions of the bedroom might make it claustrophobic for some.
What suits you is personal and only you can decide which you feel is best but each maker has normally got a variation on each in their range so the choice is yours there.