Do not use pine bark nuggets, they also float away in a rain. Pine needles are the better mulch for blueberries, and they're free.
You will have weeds coming up through ANY mulch if they weren't removed from the planting ground in the first place, and it is nearly impossible to get all of them. But using a fairly thick mulch makes them weaker and easier to pull.
I'm not a fan of any kind of clever before the mulch other than plain cardboard, which is organic and breaks down over time.
