We have tested several different 'wired' microphones. Most of them are lavalier microphones, which basically entails that they can be used for hands-free operation, and often will have a small clip to attach to your clothing.
Looking at price, performance, and overall quality of the product, we recommend the following microphone:
Movo PM10 Deluxe Lavalier: AMAZON LINK
To use this microphone with Ava, all you have to do is to plug it into your phone, and it will automatically be picked up.
Of course you are welcome to try any other microphone of your choice. When looking at the different options, make sure you buy one that has a 4 conductor jack. You can see this through the 3 little black rings on the outside of the copper end.