I know this post is pretty old, but hopefully there's someone that finds my response helpful.
I too am having issues where the volume buttons only control the media. I found an app called "Volume Styles" that includes a widget. See attachment.
What's cool about this widget is that it's no bigger than a normal app icon and when clicked on, it expands and displays the control panel.
I was able to set up the widget where I can simply press a toggle to turn off the ring, notification, and media volumes (& turn them back on based upon a preset volume set up).
The widget also allows you to do other things, include adding app shortcuts.
This "Volume Styles" app/widget works well for me, as I could not find anywhere that would tell me how to change my volume up & down buttons to default to ring volume instead of media volume.