The basic way to do this is to replace the switch, as you said, and wire it up as normal. That gives you smart control of the dumb bulb(s) in the hanging fixture. Replace the can lights with Lightify and you have smart bulbs but no control; the quick fix is to put a plastic switch guard over the switch for that set of lights so they always have power.
You’ll probably want to set up Trendsetter to group the Lightify bulbs together; you can use Trendsetter for this.
Install the device handler below for your new smart switch. Set up two new rules in Smart Lighting: double tap on the top of the switch (button 1) turns on the Lightify group, double tap on the bottom of the switch (button 2) turns them off.