I live in a rented house and the bathroom is the size of your average double bedroom. It's got a low slanted ceiling but the walls are tiled white and navy as is the floor (large white tiles with grubby grouting separated with navy diamond shaped smaller tiles).
We have the door and shower built into one wall, the sink and toilet on one and the bath on the other. There's only really room for two tall but thin storage units and there's absolutely no other storage apart from the window sill in there.
How can I make it look a little less sparse and add more storage? Even when it's tidy it still looks grubby and messy due to the huge lack of storage and grouting. Retiling isn't an option and the bathroom itself hasn't been touched in over 15 years.
The next time you are in your bathroom observe how much vertical space in your bathroom isnt being used. Typically, the space above a doorway is vacant. Especially, if you have higher ceilings than the minimum clearance you can install decorative storage shelves to house bath tub salts, scrubs etc in a decorative basket. If you arent concerned about décor, use the shelf for storing extra toilet paper and cleaners to free up valuable storage area below the sink