Starting a sourdough

I've been making yeasted breads for a long time now and I think my bread is pretty good, even if I do say so myself. There's always room for improvement though so now I want to try my hand at making sourdough. Part of my simple living philosophy is a desire to make as much as I can here at home and to buy fewer products as the years go buy. I use a very good French yeast now but I can no longer