You may use arrowroot starch instead of tapioca, but I have not tried this yet; potato starch may work too. For salt, I use Himalayan salt because it has a wider mineral profile than ordinary table salt and because sea salt is now (sadly) under scrutiny for having plastic in it. If the pudding hasn’t thickened enough after lengthy heating and stirring, remove 1/4 cup of pudding from the pot into a small Pyrex or ceramic bowl or cup. Stir in 1 Tablespoon of starch and blend til smooth and thick. Add this back to the pot and continue stirring with whisk til smooth and thickened.