Are you reusing existing furniture, or buying all new?

The best "style" for any small room is … uncluttered.

In a small room, you can get more storage by going vertical -- tall chest of drawers rather than low dresser w/place for bench/knees to sit in front of mirror.

Going industrial with the paint could mean walls and ceilings and doors all one color, even different shades of one color -- such as a light and/or medium gray.

You could go all out boho with the bedding.

But go industrial with the furniture:

Using black metal -- such as for tall thin lamps and a metal headboard -- could help create an industrial look, as could using two drawer filing cabinets for end tables (or with a third smaller top drawer). Since some lock, you'd also be providing a more secure place to store sensitive documents and/or small valuables should any of your guests prove to be snoops.

On a low budget?

Consider shopping Habitat for Humanity Restore Stores, Good Will, local charity thrift store and other used stuff stores -- such as consignment shops an even antique and more - stores.

You might want to avoid buying upholstered furniture (with the exception of items that could be reupholstered simply by removing a plywood seat w/cushion and cover that can be recovered easily as a DIY project), but other items can be worth considering.

All you need is a chest of drawers, a couple lamps, and some bedding. Pick bedding you love at first glance, whatever it happens to be. Avoid the 5, 8, 12 and 16-piece bed in a bag sets, just get two bed pillows, sheets and a comforter or duvet with washable cover.