I have lived in some very small spaces and figured ways to make the most of those spaces as far as comfort, function, and storage go. You can do that, too, if you think creatively, and are willing to sometimes sacrifice form for function.
If you have high ceilings in your studio space, a loft bed might be the right thing. I would make sure you have at least three feet of room above the bed, so you can sit up, roll over, and make sure you can use the bed as you like. I recommend having a professional build this, or you could find yourself crashing in the middle of the night, and that’s not fun.
Under your loft, you can have hanging space for clothing, a dresser, and perhaps a desk. You can purchase wire shelving units that attach to the wall, and some of them come with clothing rods. You could have a sofa under your loft, but if your studio space does not come with a closet, you will need the under bed space for storage.
If your goal is to have a more adult looking, yet still practical space, try getting a sleeper sofa, or a day bed. It can be folded up or made up during the day, allowing for seating for yourself and a guest. You can have a small table that doubles as a desk. Underneath the table, you can tuck drawers on rollers for optimizing storage space. Look for a table that can be made bigger with leaves, or smaller by having sides that fold down.
Think of creative uses for things. You can shove two chairs under the ends of the folded down table, and use the other two as bedside tables. Shop for ottomans that come with storage in them; they can double as a coffee table, work space, or dining table, in a pinch. An old steamer trunk is attractive, sturdy, and spacious storage.
Think vertically for storage. Baskets and canvas drawers work beautifully for storage on shelving units above the bed and table. Many options for shelving units are available in your local home improvement store. My favorite is wood laminate shelves that are completely adjustable for height. There is a brace that gets screwed into the wall that has slots in it for putting in the brackets that hold up the shelves. Have a professional install them. The shelves come in a number of lengths and depths as well as finishes.
You can also get inexpensive wood laminate cabinets with sliding doors that fit those same wall braces. They just hook into the slots in the braces where the bracket ends slip in for the shelves. They can keep clutter hidden. One thing about a small space is that it curbs a person’s desire to shop, and being frugal is never a bad thing.