When I had strawberries, I used shredded bark and/or pine needles, but only a light layer. I used newspaper as the main mulch, then covered it with the bark for looks. Worked quite well. Probably get a lot of objections to pine needles (they SELL it out west as pinestraw), but haven't had any adverse Ph problems with using that, either. Like I said, if you soil is acidic, add lime to neutralize.
My strawberries are doing extremely well mulched in with pine straw several inches thick. My soil is pretty Ph neutral, so any extra acid isn't hurting them and may even be helping them.