As far as the OP question, when we bought our LTV Libero, we looked at virtually every brand of B plus out there, finding the floorplans online, then narrowing in on the layout we wanted. Then, after that, we narrowed in on the brand. To have a separate bedroom and living area, we narrowed in on a rear bed and front kitchen/lounge. To have an office in the bedroom, you probably need a convertible (sofa) bed, or perhaps a twin bed, or a rear slide (like Winnie View Profile). But to have a true fold down office/convertible bed, it might require some custom work, not sure if there will be many options that have the office built in. Or if you are okay with the office in the front living area, then it might be a matter of using/converting the dining table into an office. Coincidentally, this article just came out today about a company that does fold down offices under the bed.
https://camperreport.com/living-vehicle-solves-rv-mobile-office/