GTD - designate next action for a project

Hi all,

I'm working on implementing Get Things Done in notion, and they have the concepts of tasks, and projects. Easy that far, just have two databases with a link between.
But they also have that one task per project be designated the "next action", to be done next.

So far I've solved this by creating a "next action" property of the project database, which is a link to a single page in the task database. But I find it a bit annoying to set this, as clicking an empty "next action" gives you a view of all the tasks, regardless of project, rather than just the tasks belonging to a given project.

Has anyone come up with an easy way of doing this, either by filtering in the project view, or by creating a radio-button of some sort in the task view that only allows one next action property for each group of tasks?