I think start with some nice new bedding that you love. I would get a proper lamp not a salt lamp . Can you give us at least the meausrements of the room.I like to choose wall color from the bedding and also the drapes .Do you need shelves for something? IMO shelves will just make the space even smaller but some art could be a big improvemnt . I am not sure how old you are but you coule if money is tight do a couple of framed posters or even go to Ikea and see what they have for art. I don't think the floors are horrible and I am not sure a bigger rug will work.

I bought black sheets with black pillow covers (that you can see in the picture), white sheets and also pale pink sheets.

Unfortunately my duvet is single 150x200 and it covers only the bed, but I don't mind since I'm sleeping alone and i have some different colored duvet covers.

I don't know if it's worth buying a queen size duvet ?!

I think art on the walls will give you the biggest bang for your buck, if you choose carefully. Do you have a thrift store (or IKEA, as Patricia suggested) in your area? Sometimes you can find cheap art there.

I've also used fabric instead of art as a wall hanging - and fabric on the wall could help soften the space and is generally cheaper than art.

It might be too big of a job, but you might want to swap the bed and the wardrobe. You could then make your bed look like a daybed with cushions against the wall.