Studio Flats
One room doing four jobs. Everything here is chosen for that: furniture that folds away when it isn't in use, storage that goes up rather than out, and dividers that make a sleeping corner without building a wall.
The two things that change a studio most are a fold-down bed or desk — which gives you the floor back every morning — and a room divider that stops the bed being the first thing you see from the door.
If you're starting from empty, a studio starter package is cheaper than the same pieces bought separately and takes the decisions out of it.