That loft bed trick is a game changer for small spaces. We hung curtains to split rooms and give each person a private corner. It costs almost nothing and you can move them around easy.
Tried the curtain trick in my old apartment and it never blocked sound or light enough. Felt like we were just hiding behind sheets instead of having real walls.
Actually tried using bookshelves as room dividers in my last place, gave up when they just became dumping grounds for everyone's random stuff. My version of personal space was just staring at a tower of mail and old coffee mugs... not exactly peaceful. Might need to go back to the curtain idea, just with thicker fabric this time.