I find a habit tracker can be great complement to a task manager. They’re useful for getting specific activities to a place where they’re performed without any prompting (e.g. flossing teeth, journalling, reading what’s been added to Instapaper).
Doing something consistently for 40 days is typically long enough to instil a new habit in my experience.
I’ve spent time with most of the popular habit tracking apps, and my tool of choice is Streaks. I like its balance between simplicity and functionality. It integrates with Health Kit and has great AppleWatch support, including the ability to add a complication that shows which activities have been completed.