Hey supportive mom...I tested all the toothpastes now. I really recommend trying the sensodyne since it is available in stores easily. I have used it a few times now. No gagging and no burning. Maybe you can get a sample from your detntist to try it before you buy it like I did.
The biotene was a no go for me as it burned my tongue. I also tried Colgate "gentle mint" sensitive---gentle my butt!
Hope you are succeeding on your toothpaste search.