https://www.amazon.ca/Avantree-Bluet...9BHV6HW7?gQT=1
What about something like this? It has a built in mic and speaker, essentially should work very similarly to a speakerphone in a conference room.
FM transmitter is built in as well, but optional.
I haven't tried it, but if I were in your shoes I would probably go for something like this.