I got one of the couch futons. it even has removable arms. now the futon can be a little firm, but there is storage beneath. so i got a feather bed and put that with the sheets etc. in its storage.

Why don't you buy a comfy sofa bed, futon is hard !

King mattress seems like it would take up way too much space to only be used by an occasional guest. I didn't know they still made futons. I had one in the 90s when I was trying to save money and didn't have much furniture and it gave me a sore back. Go for a sleeper sofa or sleeper loveseat. Or how about an air mattress if you don't have many sleep overs. You can deflate it when you need the space.

my problem is the air mattresses we bought kept deflating. if you have adults, they may well be uncomfortable with it on the floor. i have never been the right size to be comfy on a fold out couch-there is always a bar sticking somewhere. When you put an airmattress - if you can get a non leaking one, or a featherbed/foam on top when made, it really is quite comfy. the modern ones are now made to look like couches and even have the height to make them comfortable.

I would say keep the king mattress. As both a guest and a host, I have found most people prefer a regular mattress. As a guest, I really appreciate a good bed and would have an uncomfortable night on a futon. Some air mattresses are ok but many are low and it is hard for me with my back, to get up and down. As a host, I like to offer a comfy bed and many guests have told me how well they slept when visiting. Most younger people can sleep on anything, but as you get older, a bed is nice to have. As to a sleeper sofa, many offer an air mattress instead of a thin foam one and I hear those are comfortable too. My Mom got hers from Lazy-Boy. Might be something to look at.

If u rarely have guest n r actually using this room as a dressing area, then I'd get a futon to give up the room u want on a daily basis. It just depends on ur use of the room. I think U should do what's comfortable for u. Besides u don't want to make it to comfortable for guest since u do want them to leave. Lol. :)