Here are a couple of youtube videos that might help our cellists and bassists.
My thoughts on vibrato are these: There is no wrong way to do vibrato if it sounds beautiful and doesn't cause the player any pain or discomfort. There are so many different approaches to vibrato because people have different builds physically and want different musical effects. I try to learn many different technical approaches so I can add them to my vibrato "toolbox," and when I need a specific vibrato to achieve a specific sound I have it at my disposal.
That being said, Happy Practicing!!