Bluetooth mic board for pen or pencil case

Greetings, I need a bluetooth board with a rechargeable battery that is small/thin enough to fit in most pen/pencil cases. I don't have an exact specification for the dimensions, as long as it fits most pen or lead pencil cases. But do, please, let me know what dimensions you plan to use. To save space, this bluetooth board is to be designed for a mic piece only. The device must also have the basic bluetooth functions such as on/off, connect, discoverable, and rechargeable. Let me know if you have any suggestions or need to know everything else. Thanks for looking!