It is far more common with basses to see multiple volume controls or blend controls, as opposed to pickup selector switches.
For the typical player, it is important to be able to switch pickups quickly on a guitar to go back and forth between different sounds (Clean and distorted, for example.), but it is more important to be able to mix pickups in the right proportion to get the tone you want on a bass.
You can wire your bass any way you want, however.
Choosing a pickup selector switch over multiple volumes or a blend does offer a few advantages.
Resistive loading from the pots is kept to a minimum, allowing you more output and treble, and since there is only one signal to control, the wiper terminal of the volume pot can be wired to the output, keeping a constant resistive load parallel to the pickup(s), regardless of volume setting. This means that the tone stays the same at all volumes.