My magic mirror that I'm building is intended for the bedroom, so similar concerns.

I did end up going for a pir sensor and have it set up up in my office,( no glass or frame yet, just the pi and monitor) and it seems to work with well MMM-GoogleAssistant controlling it.

https://www.amazon.com/gp/aw/d/B07GJDJV63?psc=1&ref=ppx_pop_mob_b_asin_title

As far as a microphone, I wanted to include a selfie camera in the build, so i ended up getting a webcam that came with a microphone.

https://www.amazon.com/gp/aw/d/B08D3S4YPQ?psc=1&ref=ppx_pop_mob_b_asin_title

As far as a speaker, the monitor I'm using does not have HDMI, as it does not have speakers built-in. Haven't decided on what I'm doing long term there. For now I'm using a bluetooth speaker and using the pi to connect to it