As far as how to get a lighter touch...just try it. Experiment with various amounts of pressure with the left hand. Use the weight of your left arm to do most of the work, you really don't have to squeeze much at all.
In fact, it is possible to play with just fingertips, leaving the thumb dangling in mid air! Not something you would use on a regular basis

but it will help you understand how to apply more force with the downward pull of your arm. The more vertical you position the neck (go look at Bill Wyman with the Stones) the more downward force from the arm weight and the less you need to squeeze.
Here Bill has the bass up on his chest and the neck way up almost like an upright bass.
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Here it's slung much lower, but still at about a 45 degree angle.
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You can feel the arm weight without holding the bass, just by holding your arm in a "V" shape with the elbow down and forearm up. The higher up the forearm gets, you will feel the arm get heavier.
This is true of a lot of "modern" sounding basses. My Steinbergers expose every single bit of sloppy technique.