Cool fish safe invertebrates?


After loosing my potters wrasse to my CB shrimp (killed him while he was sleeping in the sand) I am wondering if there are any fish and coral safe invertebrates that are big and friendly. I love my CB shrimp, but I definitely cannot keep an invertebrate that is going to kill my fish. I want something that will get similar to size as a CB but not as aggressive, any ideas?
If it's shrimp your looking for, go for either a plain cleaner shrimp or a scarlet shrimp. The scarlets are brighter, but they also like to hide more. On the other hand, my cleaner always flies on my arm when I'm doing maintenance to clean me. I also have a scarlet, and he's been becoming more brave and actually comes out of his hole for feeding time.