I am also using Android TV app when I need voice / typing assistance.
You can try adding a Bluetooth adapter and then buy the Mi remote with Google Assistant button. But I am not sure whether you can make it work. Tech Singh had an Air Mouse mentioned in one of his videos. I do not remember whether it can work with Google Assistant.
Your best bet is the Android TV app. I don't like it personally, but it is feature rich. If I remember correctly, neither hardware remote, nor the app has a mute button. So sad and out of standard.