Nice idea for a project!

I have opted to use Home Assistant (https://www.home-assistant.io) along with an alexa integration for most of my home automation. I am sure this would do most of what you want (assuming there is compatible support for your smart-switches). I can already think of a case where you could use Home Assistant to set a timer once you turn on the blanket that would turn it off after a pre-set amount of time.