I didn't add it to the bom, because depending on how you plan to wire everything up, which one to use ranges from "it doesn't really matter/use whatever you have lying around" to "this specific model"

If you plan to go the push button route any relay board marketed for use with an esp32 or arduino should work fine. The one I specifically used doesn't seem to be available internationally on Amazon, but this one is basically the same: https://www.amazon.com/DIYables-Arduino-ESP8266-Raspberry-Channel/dp/B0B1ZHXXXD/ref=sr_1_2?crid=2TBHRZL1588SL