I am turning some of m,y lawn into garden areas for shrubs and bushes etc.

Cut the turf out today using a turf cutter as it was going into someone
else's yard.

What should I now be doing to prepare the area? I was going to rotary hoe
it and combine it with some mushroom compost but I am concerned about the
existing couch roots that remain and I fear that they will grow back in
amongst the new plants.

I plan to put down weed mat but I know that it is 100% fail safe with weeds
so I guess couch will be able to grow back through this stuff.

What should I do? Put down plastic instead of or with the weed mat?
Something else altogether?

Thanks,

Craig