Caudabe Sheath is an excellent alternative. Size wise, it should be close to your Apple silicone case but with a much more robust material. It's exactly what a case needs to be.
It's essentially TPU with a textured finish, but since I know forum members on here are particularly finicky, you may not like the texture. If that's the case (heh) I don't really know what else to recommend aside from cases you can find on Amazon (Spigen and Torras make clear back/TPU cases with a smooth finish that feels nice to the touch)