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I'm not sure how much this will help, but Comcast offers large button remotes to aid with accessibility free of charge.
https://customer.xfinity.com/help-and-support/cable-tv/large-button-remotes/
It might help as a temporary measure at the least.
As for something a bit more permanent down the line, Googles new Google Home will soon have Netflix capabilities, although it doesn't yet. Once it does, it will be a bit costly (120ish for the device, 15-30 for a chromecast), but that would allow casting to the TV though voice. It currently works for Youtube videos.
Some cheaper ideas, depending on what you feel comfortable with:
Get a second Comcast remote, crack it open, solder a more accessible friendly giant button to the voice command, mount the whole thing in a new enclosure.
Pick up a cheap used android phone that has an IR blaster (I've done this with a Samsung Galaxy S4). Set it up with a remote app, Tasker and Autovoice.
This setup can be pretty easily configured to control pretty much any remote controlled devices completely through voice, with the cell phone picking up commands from anywhere in the room.