BLE + Sensors + Battery in a plastic. We already done 85% of your product.
SensiTHING Environmental Monitoring Module with Wireless Charging Capability
Application note: How to add AA battery To SensiBLE 1.0 or SensiSUB 1.0
Why lithium batteries do not suit Wearable IoT application…or do they?
From Bluetooth Low Energy to Cloud : SensiBLE IoT node use case