90% of my OmniFocus is done via my Apple Watch, so I can definitely help here!
What I do is create a specific Watch perspective (creatively named “Watch”) and have it set to show flagged task, due tasks, and tasks with a specific tag (such as “Next”). That is then what I choose to display on the Watch face.
There are definitely MANY limitations to the WatchOS App, but I’ve figured out my own workarounds over the past few months, and having a workflow centred around the Watch is very possible.
Alternatively, if you don’t want that as a perspective to be the list you display, you can start flagging tasks instead, as these will show separately on the Watch app. This will require you to change the way you use flags and the “next” tag, so this may not work for you.