Greetings,
I have expertise with such systems. In fact I am working on a wearable currently which has BT, Sensing, Battery Management. Please see my profile for more details.
I think I understand what you need - however it involves a lot of work - circuit design along with choosing the right components, layout, pcb fab and bring up, firmware, testing & debug. It will be good if we can discuss the specifics. It will help estimate better.
Look forward to hear from you.
T & R
Alok Pugalia