This is free agency, the only option is over-priced and/or risky. Matthews will be just 31 this season and presumably starts the season squared away health-wise and position-wise. Him whooping some ass doesn't require some comeback player of the year narrative. If you think best case scenario for him is KGB at this point then ok I guess. I think there's more than that in the tank.
You can and should sign a starting-caliber CB anyways but it won't matter if there is no pass rush. Its easy to imagine a much improved pass defense just with a two-armed Matthews and two-handed Perry.