Keeping kids clothes organized?

I have two girls sharing a room right now. Possibly we'd be adding another two girls to the room. It's a large room,and there's plenty of floor space -although we'd have to add another bunk bed. Right now my 13yo has a dresser, she has the bottom two drawers empty ,awaiting a new sister. My 7yo has wooden cube things in the closet, and I'm looking for some of those collapsible cubes for her to keep the clothes in the cubes easier. She tends to cram everything in the cube in one messy lump,and stuff ends up falling everywhere. any other suggestions? I'm thinking I may need another dresser, but I'd like to keep as much floor space available for playing room. how about under the bed storage - anyone do that? Other suggestions?