I'm assuming this is the aluminum model. If so, I think at most you would just need is a screen protector. I typically don't recommend the protective cases that surround the Apple Watch, as they add weight/bulk and they can trap in dirt or debris that can actually damage the Apple Watch casing.
I wanted the Zagg Luxe screen protector for my AW3. Since I couldn’t get it, I picked up a Caseology case for the watch body. I found it on Amazon. Until I get the screen protector I want, this is cheap insurance IMHO.