That looks really nice, Quartz.
I still would find making and unmaking the bed a bit of a pain, but otherwise it looks really comfy and I’m sure the lodger could leave it open permanently if they didn’t want to keep doing it.
We bought one of those for our living room three years ago. They were called Fogelbo back then, and they were about 600 euro’s/ dollars. . They were perfect for guests to sleep on, (not too perfect though 
) and surprisingly easy to change in to a bed. You can’t have a high piled carpet under them, though, as that interferes with pulling/rolling the bed part out. We often rolled the thing out just to watch TV together both with our legs on the bed.
We did have bad luck with ours though. It broke after just three years, I think because we didn’t quite install it well.
Ikea has lots and lots more sofabeds. It is kind of their speciality.
Almost anything I’ve had from Ikea has broken after ‘just three years,’ and I’m inclined to think that it’s not because of my faulty installation. If you want disposable furniture that you’ll get rid of when the lodger leaves, then buy Ikea, but if you want it to last, I wouldn’t recommend it.
Also I find all of their couches much uglier in person than I do online.
A sofa bed would probably be more practical but boy have I slept on some crappy sofa beds and they all didn’t have the dreaded middle bar of doom either. I’ve slept on around a dozen of them and they all sucked. I’m sure they make comfortable ones, maybe I just have had bad luck.
also - if you get a futon then make sure you get a good futon mattress as well. what might be fine for the occasional guest can get uncomfortable night after night if it’s your only bed.
What about something like a daybed?
Like the ones here: http://www.daybeds.com/
Basically it’s a regular single mattress on a platform, and you dress it up with pillows to use as a sitting thing during the day.
You can use the underbed area for storage, or for a trundle mattress. I don’t know if there are varieties which lift up to turn it into a king-size - I seem to recall seeing such a thing, once.
Reminds me of when I went to visit my mom when she went back to grad school (I would have been ~20). She had a day bed and she and Pop huddled in that while I slept on the trundle bed (pulled out but down at floor level). Pretty close quarters!
This animates a king-size trundle:
http://www.apartmenttherapy.com/images/uploads/pop-up%20trundle.gif
Mmmm, whipped beans.
Not just whipped, but “uncle’d whipped beans.” It’s a local specialty.
Being a modern-day gypsy, I have slept on them all.
My favorite was the sofa I bought myself - it was a single cushion for the seat with 3 oversized pillows for the back. The single cushion was about the size of a twin and I slept on it comfortably with or without the back cushions on it. (I had a problem sleeping in the queensized bed alone - it freaked me out). During the day I just folded up the comforter and fitted sheet, and tucked them in the closet with my bed pillow. The cushion never got squished down from the constant use - it was a dream.
I would suggest a twin as a daybed or a couch like that - useable for both of you no matter what you decide.
What kind of lodgers would this be? If you’re thinking it would be students from the local college/university, you need to consider a desk space as well. If you rent to grad students, they are, on average, more likely to want to study and sleep than socialize in their rooms, so the bed is more important. If your potential lodger is a working person, then potentially entertaining and wanting a place to relax and watch TV is more important, so a couch becomes more desirable.
While some sofabeds can be comfortable, I have never slept on one comfortable enough to want to sleep on it for weeks at a time, let alone a year (which I assume your lodger’s lease would be!)
I think a day-bed is the best option to give a couch+bed because the important part for comfort is actually the bed, and the mattress can be of any type and quality to keep your lodger happy. Futons are OK, but given a choice of similar lodgings, I’d take a day-bed over a futon (and a futon over a sofabed) any day!
I love this site. I’ll probably never buy anything from them but the engineering is wonderful.
Desks that turn into beds, etc.
a little more specific link to my favorite beds here
That’s what I use in my very small spare bedroom. Works perfectly and is INCOMPARABLY more comfortable than any sofabed I’ve ever slept on and more comfortable than most futons.
My order of preference:
Day bed (due to comfort)
Futon (only if you want something to fold into a double space- if just a single stick with a daybed as they’re more comfortable and you can store stuff underneath)
Absolute last resort: sofa bed
I’d prefer a daybed over a sofabed you have to pull apart and usually has a crappy mattress. Futons generally have to be folded and unfolded too. A day bed is a real bed, you just toss off the back cushions before bed.
Hadn’t thought of a daybed - that would be a great choice! Or a single set up as a daybed, same thing pretty much.
If you’re talking about college students as lodgers, I’ve seen a terrific double-decker with a single bed on top and a futon sofa underneath. It’s what I’d probably get if I were that age and moving into a single room or dorm. Something like this, although that one’s probably not up to par.
A low-cost ordinary bed may not last forever, but low-cost sofa-beds often deteriorate into something quite unusable in a fairly short time (the cheaper ones are, I think, designed for occasional use only).
If there’s enough budget for a mid-to-decent quality one, ignore the above.
I’d go with a futon. This being said, my reasoning is because I recently stayed with friends for a while, and they have a really comfy one. Very sleep-conductive. 
those are the most coolest uberest thingy dinghys evah! (highly technical terminology of praise)
I’ve slept on one of these and found it quite comfortable - I see that you can choose matresses, and I’d assume this was with one of the more expensive models. I mention this one because the beauty of it is, it’s comfortable enough to sleep on in the “sofa” position for just one person (that’s how I slept), but can easily fold out to a double bed if the occupant prefers more space or has overnight company. So if it was me, I’d look for something in that basic style, and let the lodger decide how to use it.
Another vote for a daybed with a really nice mattress. The Hemnes daybed from Ikea is really sharp looking and would provide storage underneath.