For a speaker, I picked up one of
these for $5 at a local store. Has an onboard amp powered by a battery charged via microUSB (you can leave it plugged into the Pi to keep it charged.) Note the audio cable is only about 4 inches long, so it has to be right on or next to the Pi. It does not have volume control, so you need to use software to turn it down if necessary.
I've done voice control with my Pi also, and I used a microphone built into the cheapest Webcam that Micro Center had several years ago. Sorry I don't know the make or model, but what I'm saying is that almost any USB mic should work, even if it's integrated with something like a webcam. You can't plug a microphone into the audio jack, as that is output only. Your two options are USB (easiest) and an Analog to Digital Converter (harder.)