Hello, Boomer--So sorry that you are in this predicament too. I am the Mom of a 40 year old man with ALS who has been non-verbal autistic all of his life.
So I can only speak from observation. Wally, Jr. decided he wanted a g-tube and needed to be cleared by a respiratory doctor before he could have anesthesia administered. Bad news--CO2 levels too high. We took him to a doctor in Newark, NJ who specializes in non-invasive respiratory treatment.
He recommended a Bi-Pap. Our doctor here wrote up the RX and our insurance came through. Wally, Jr. had been on an oxygen concentrator for a time and that was helpful. We weren't even aware of the weakening of his chest muscles--it seemed to occur so gradually. It took awhile to get him used to the Bi-Pap. Started with a mask, which he didn't tolerate at all.
The respiratory people sent up a less cumbersome interface--more like the cannula that he used with the oxygen concentrator, only thicker. He began to tolerate that and what a difference that has made in his life. He had stopped using the computer to communicate and now he is back to typing and faster than he did before. He asked his Dad to take him to the ocean and he was able to go to Acadia National Park in Maine--the Schoodic Point area of the park. He smiles alot and just feels so much better. I am sure he is clearing the CO2, but has not been tested for that again yet. He uses the Bi-Pap at night or when he isn't feeling well.

I hope you will have a chance to feel better too. Best to you.

Wally's Mom