There are two Z-Wave bindings available. The 1.x binding will work with your existing items config. You’ll need to update your item definitions to work with the 2.x binding. I would suggest going with the old binding to get everything working, and then migrating once you feel comfortable with OH 2 concepts.
In Paper UI, go to Configuration > Services > Extension Management (configure) and make sure that “Include Legacy 1.x Bindings” is enabled. Now you should see both versions in the Extensions list. Install the Z-Wave 1.x binding, and then check the zwave.cfg file generated in conf/services.
Here’s a thread with some more useful info: https://community.openhab.org/t/getting-started/4228