Try this third-party app called Lyd:

https://lyd-for-sonos.app

Why a third part app?? Don’t Sonos have one themselves?

Currently, Sonos does not have an app for the Apple Watch. Nor do they have one for the Android Watch.

Probably not yet enough demand for a native iWatch App, perhaps? Plus it helps other small businesses/developers too, if they decide to then fill those market gaps.

They claim it should be more than speakers, easy accessible for all users and they don’t have the app to one of the biggest brands.

Not a perfect match…

I’m disappointed  

Have you tried this? It worked for my Android phone and watch.

On the phone, open Sonos App Settings > App Preferences and turn on “Show Notifications,” “Show Lock Screen Controls,” “Control From Other Devices,” and “Home Screen Volume Control.” (The settings might have different names in the Apple phone app)

Once I did that, Sonos appeared in my watch’s music app. I didn’t need to install any extra apps or widgets or anything.