I use idli rice. It looks like parboiled rice, but short and round. Proportion is 3.5 to 1. I soak it in the morning, grind in the evening and allow to ferment overnight. Even with mixie grinding it is soft. I realized that for good soft idlis the amount of water in the batter has to be just right. More water or less water makes it hard. Also, the urad dal has to be ground to a very smooth paste and rice to a somewhat smooth paste. Not too rough again, and not too smooth also. Also, before making idlis, dont mix the batter or all the aeration due to the fermentation process will go away. Just pick up batter and put it in the idli moulds. Like others, I use this batter for dosas also, by mixing water, from the second day.