How do I pair multiple devices with my iPhone 8? I have hearing aids paired, need to also pair a Bose speaker.

To the best of my knowledge, there isn't a limit to the number of different devices you an have paired to your iPhone.

See these instructions:

Pair a third-party Bluetooth accessory with your iPhone or iPad - Apple Support

Pairing should not be an issue, please see the pic below. Pairing multiple Airpods with Multiple Devices. You may not be able to connect all of them simultaneously but pairing not restricted.

Voices