^^^ This, this, a thousand times this!
Give yourself a couple hours and sit down to this web site, the writer is a member of this forum.
It really is very well written, and will teach you a lot about what's available.
And to reiterate what's already been said...
Practice dynamic control with your fingers.
Going from classical guitar to electric bass, I already had finger dynamic control well ingrained in my muscle memory.
Very different feel from acoustic guitar to electric bass, but the principles of finger pressure, attack angle and release angle are the same.
Finger pads or finger nails, knuckle hits or finger tip hits. Soft pressure, hard pressure.
Search the techniques forum here for more better explanations..
Also, if you're coming from electric guitar, try using a pick with your bass.
I don't usually, but when I do, it is noticeably easier for me to control dynamics since the material hitting the string doesn't change density much (like different fingers will).
Of course, I'm not very good with a pick, so take that with a grain of salt.