A slicker brush is probably the best. The comb would also be good. it should not hurt once the mats are out and you are simply using it to prevent future mats.
Hopefully you will be able to find someone who remembers that the customer should get what the customer wants (if at all possible). Groomers all too often hear owners say that their pet is not badly matted when the truth is just the opposite. That is why many are skeptical when you say I only want the mats shaved out. We as a professional, do not want the finished product to look like a 2 bit hack job. (I really did not mean to turn this into a "lecture") Just keep looking for a cooperative groomer.