You could do it with both, though since I'm more familiar with ESP8266 that seems easier, plus most people always have WiFi on at home but not Bluetooth, so that saves wasting unnecessary battery. You could theoretically just use one clone NodeMCU board(they're like $2 on AliExpress) and the Blynk app. If you need I can post a simple sketch to get you going and you'll just need to put in your blynk token and whatever you need for the relay trigger, etc. Blynk is definitely an app worth checking out if you want to control Arduino/esp type devices OTA and don't quite want to dive into android or IOS developing to create your own app or widget to control them.