For my cortana, ok-google setup, I paired a Kangaroo pc with a usb microphone, works fine. Any audio going to the display is transmitted via bluetooth to more adequate speakers.
https://www.amazon.com/dp/B00IR8R7WQ/ref=cm_sw_su_dp
Used the one Amazon posted in their instructions, $2 - it works great
I got this one for $2 but took about a month to arrive. Works well though.
Kinobo - USB 2.0 Mini Microphone "Makio" Mic for Laptop/Desktop PCs - Skype / VOIP / Voice Recognition Software https://www.amazon.com/dp/B00IR8R7WQ/ref=cm_sw_r_cp_apa_LpvxxbX5XADXS