5v supply amp modules?

If you want to run a RPi Zero, then this is possibly one of the best options. You can select mono output in the RPi software. You'll need a good powerbank:

https://www.infineon.com/cms/en/product/evaluation-boards/kit_40w_amp_hat_zw/

Alternatively, I use a number of these in BT speaker builds (stereo, not mono):

https://www.aliexpress.com/item/329...ab!66517632763!sea&curPageLogUid=28eEP4PAPinK

Here's a mono amp:

https://learn.adafruit.com/adafruit-max98357-i2s-class-d-mono-amp


Apart from the RPi solution, I'm guessing you'll also need a 5v BT module:

https://www.aliexpress.com/item/100...00026884840784!sea&curPageLogUid=K5KdaQvccNZ3