To the best of my knowledge, Android supports Bluetooth heart monitor sensors without the need for additional drivers. I personally use cost-effective heart and cadence sensors from Magene that I purchased via AliExpress.They work seamlessly with platforms like Peloton, Wahoo, and Polar Beat.
While many sensors offer unique features, their core functionality remains consistent. For further details, you can refer to this GitHub repository by Polar.
I haven't worked with Unity, so I can't provide insights on that front.
I understand the challenges of being a solo programmer with limited resources. In my opinion, if you're targeting a niche audience like indoor cycling enthusiasts, having a standout feature could be beneficial. If you're planning to monetize your product, this could add significant value. Alternatively, if revenue isn't your primary goal, consider open-sourcing your project. This might attract other developers who can contribute and elevate your product's development.