I had an unmitigated success with my sourdough starter today. Two round loaves of something resembling my rustic bread  but with my starter instead of yeast.
I pulled the starter out and started feeding it every 12 hours beginning Thursday evening. During that time I kept it in my oven with the light on so that it was in a 80 to 90 degree environment. It seems to require that: without it, I don't even get a doubling in 24 hours. With it I get nearly a tripling in size in about 8 hours. We must keep our house too cold.
I made my final dough Saturday night and placed it in "the cold room," a poorly insulated room in our house that stays between 45 and 50 degrees this time of year. In the morning I gave it a fold and put it in the oven with the light on again to take the chill off. Gave it two hours, folded, two hours more, then shaped them. After a three and a half hour final rise I baked them. Amazing how much pop sourdough loaves get in the oven. They came out great.
Thanks for all of the advice and encouragement everyone, particularly Sourdolady. The continued effort paid off.