ran across this, not sure how well it works, but if you get it please let me know
I couldn't find one with a manual switch. But I did find this type that may work for you:
Smart WiFi Wireless Essential Oil Aromatherapy Diffuser - Works with Alexa & Google Home – Phone App & Voice Control - 400ml Ultrasonic Diffuser & Humidifier - Create Schedules - LED & Timer Settings