During experimental periods of my life, I have brushed with Baking soda and peroxide, or with myrrh and some other herb, I think it was goldenseal. Would those combinations avoid the glycerine problem? Also is the link you provided the only answer to 2), or can you recommend other diet or supplementation to produce enamel?
I do not believe there is glycerine in any of the items you mentioned.
You will require sodium monophosphate. There are a number of companies who manufacture it. I believe the Swanson price is the cheapest. You need about a gram a day in some water. I do not know of another source, but perhaps there is one.
For $8, you don’t have much to lose.