The XIAO Sense boards manage to fit a microphone, and since I'm looking into ANC for Tetinerary, it makes some sense, especially since the Tetrinsics are planned to be infront of the ear.

I wasn't able to find anything decent for a decent price on JLC's part library, but I have found 2 sub-£1 options on Digikey that have the full 20 - 20,000Hz of range and relatively high SNR ratios along side a -26dB sensitivity. According to the Infineon datasheet, this allows capturing the full dynamic range with 16-bit PDM, which is the max the nRF52833 supports. Coincidentally, the 833 samples at 16kHz, just like the proposed speed of the Field Orientation Control loop.

Digikey's XENSIV page was the first thing I found on my search and the IM69D120 does seem like the best option, with a 69dB SNR. 

The SPK0838HT4H is cheaper and has a 64dB SNR, which seems more typical as most others I've seen are 60, 63 and 64dB. It also has the mic port on the top instead of the bottom, and unlike most, doesn't seem to have a shield and seems to be made out of PCB:

There's also the IM70D122 which has a similar but not identical footprint and has IP57 water resistance.

These microphones need 3 pins, meaning that the PCB would need 19 / 20 available GPIOs.