Are there any specific Apple Watch models for lefties? Well you don't really need one as the Apple Watch fully supports left handed use. When setting up your Apple Watch for the first time you will be asked to choose on which wrist you want to use it. You want to edit this setting at any moment, using one of the below methods:
From the Apple Watch
From the main menu of your Apple Watch go to Settings > General > Orientation. Select on which wrist you want to use the Apple Watch. You can also change the orientation of the Digital Crown from the same menu:
From your iPhone
You can also change this setting directly from the companion iPhone. Open the Apple Watch app > My Watch > General Settings > Watch Orientation.