If you can find a decent boundary mic that already has a usb sound card built in, that is the route I would go. But I would still recommend if you are putting down a chunk of change on this, that you buy it from a place where you have the option of returning it. Once you get a microphone that picks up everything even at a great distance, I think you'll find your prefix mode is not enough. It is worth a try, but only if you can get your money back.
For what it's worth, pressing a single button and then speaking, is still siginificantly easier to get the music you want immediately, than pulling out a phone, waking it up, launching an app, browsing your library to find what you want etc.