I swear some are born with a good vibrato, and the rest of us have to learn it. As you probably can hear, vibrato width and intensity are purveyors of meaning in a note, and as such vary with what you want to communicate. So my trick is to practice the whole range of vibrato width by using a metronome and whole bows: very wide, with almost a 180 rotation of the left wrist, to a very narrow fluctuation, increasing the frequency by matching the metronome. Even though that is not very musical sounding, it gives you the motor coordination to control your vibration at all frequencies, without having it be a jerky, inconsistent reflex (not that yours is

). That way, you can use a very wide, sonorous vibrato on slower, lower notes, and a quicker stronger frequency in the higher registers, and in fast passages when appropriate.
Many cellists and bassists use a very quick, nervous sounding vibrato; basically one frequency for all uses. That does not serve the music well. You need to have control throughout to support your intent. You can also practice whole bow scales this way, and concentrate on keeping your vibrato intact from one note to the next. Just some more boring practice ideas, but man, they do pay off.
I have also heard bassists say that less is more w/ DB vibrato particularly when playing with others. After all bass is the foundation, and it needs to be solid.