It may be worth checking out second hand shops, in dd playroom we had a tall unit for dd toys, that had plastic crates on but I hated it as it seemed to dominate the room.
I saw an old sideboard/bookcase that can take 6 storage plastic boxes that fits nicely into the bay window and as it is the same height as the window sill it makes a nice surface for the goldfish and some of dd wooden toys. Only cost me £15, needs a paint job but does the job perfectly.