I guess you have to figure out a few things first. Who do you expect to stay over night? Single friends or family members? Couples? Young or elderly? Will you use it for a place to sleep when husband is snoring or one of you is sick? How big is the room and what else will you use the room for besides a guest room? You mention an office, so how often will you need this office if guests are there? We just moved and my choice for the extra room that would have to be my sewing room, was to put in a simple twin bed for guests. Chances are that our only over night guest will be our 4 yr oldgrand daughter, and if her M. is here too, they can share the twin, or sleep on the floor. If a couple comes to visit, Im pretty sure they would rather stay in a hotel.
So figure out what you want to use the room for, and how youd like it to look. If we had enough space in our home office Id like a nice looking couch in it so I can sit and visit with my husband while he works at home. Ive sat/laid down on some top quality futons and you couldnt tell it folded up into a couch. Some are really comfy.