Integrating Homekit with my full SmartThings setup? (2019)

You are correct, the primary method is HomeBridge. Or buying devices like the Phillips hue bridge that will work with both HomeKit and smartthings. The information hasn’t changed much.

The only thing that’s really new is now you should be able to use Siri shortcuts as well for some use cases so you can use Siri with SmartThings controlled devices if all you want is Siri voice control. But the shortcut method doesn’t give you any of the other HomeKit features.

There’s an active thread if you want to go to the homebridge route. People there should be able to answer any questions about that process:

There’s a list in the community wiki on devices that work with both smartthings and HomeKit. There aren’t many, but there are some, and if you select carefully you can cover many tasks.

And here’s the thread on Shortcuts. Setup is clunky and you don’t get to use any of the other HomeKit features, but if all you want is Siri voice control of your smartthings devices, take a look at it:

iOS Shortcut Options? - #5 by JDRoberts