There are quite a few smart televisions which will work with an Amazon fire TV stick except they won’t power on by voice that way.
If you get the Amazon fire TV cube instead, it has a built-in IR blaster which can usually turn these on and off.
But if you already have the fire TV stick and like it, you can just add an IR blaster which works with smartthings. I myself use the SwitchBot mini hub for this. The manufacturer has provided a smartthings integration which is a little clunky but does work. Basically you have to set up a scene in the SwitchBot app that will turn the TV on or off and then you can access that scene in Smartthings like it was a switch.
Here’s my report on that product if you’re interested. It lists for $39 at Amazon. The topic title is a clickable link.