Dynamic Brush Tool

Add custom smoothing dynamics to your brush. This will give you similar smoothing results as the normal freehand brush. There are a couple options that you can change.

Mass

Average your movement to make it appear smoother. Higher values will make your brush move slower.

Drag

A rubberband effect that will help your lines come back to your cursor. Lower values will make the effect more extreme.

Recommended values are around 0.02 Mass and 0.92 Drag.