Designing new earphone hardware with firmware to talk via bluetooth

I want to design and build a new earphone which will talk to my iPhone via bluetooth.
We do not have any restrictions on choosing the hardware: I am ok to use any hardware components my consultant suggest as long as it's flexible to talk via bluetooth and I can add more chips when required.

I need someone to help me to implement a firmware so I can connect from my iPhone app.

Please note I am a developer mainly experienced on iPhone side.