Now that you know how many boxes you need, you need to know how much space you have for them. Remember that the whole idea of using storage boxes is to be able to clear things away, and not to have a room filled with these boxes. You must be able to hide these boxes, away from exposed areas. You should also get the measurements of where you plan to put these boxes. Measure how much space you got under the bed, inside your wardrobe or above it. You wouldn't want to purchase boxes and still end up living it on the hallway because it won't fit anywhere. So remember to take measurements, write them down and bring it with you when you go shopping.
Many a times we buy furniture and paintings on walls which go well with our bedroom or living room interiors, the same way, it is also common to buy plastic storage boxes that goes well with the room ambience. Thus you should choose between the colored storage boxes and the transparent or plain colored storage boxes because these can affect the look of the interiors in a drastic manner. If you have a good number of colors used in your interior, it would be a good decision to choose a matching colored storage boxes and use them.