Try Wing On. I bought some hook-like door stoppers there. You can simply hang the hook-like door stopper on the door hinge to protect the door from closing accidentally.
I think the U-shape door stoppers are not very useful as they can only be placed on the side with the door handle and cannot protect babies' fingers if babies put their fingers into the other side of the door (the side with the hinge).
I couldn't find it from the Wing On net. I went to Taikoo Shing Wing On yesterday but they are out of stock. Please pm me your e-mail address and I will send you the photos.
可樂,
The one that I bought was not the one shown by PaPa. It is in hook-shape and it can be hanged on the door hinge. I don't know how to attach the photos here but I really want to show it here and let you all know how it looks like as it is a very good device to prevent the door from closing accidentally.