Hi Ilse, welcome to permies!
I hear you about fighting couch grass... it took me years to clear a fairly small area, picking tiny bits of
roots out of one shovelful at a time...
I have no daisies here except little tiny ones mixed in around the meadow... I had no idea what a daisy bush was...
https://en.wikipedia.org/wiki/Olearia makes it seem likely that they're at least the same family as whatever mine are.
I'm keen to hear how this experiment goes, I would love another option than the combined mulched path/plastic/trench that I used now.
A latin name for this 'daisy bush' would be handy, or some other more specific identifier? For that matter, can you confirm that your 'couch grass' is 'Elymus repens'?