Dry yeast amount for bread dough

I use 1/8 table spoon dry yeast for 3 lbs of bread dough. Details: dough rise 3-4 hours at minimum 70C (21C) room temperature - even one less degree will prevent rise. I use no salt of sugar at all. Most important for dough is room temperature during preparation and rise. I noticed, the ideal room temperature interval is between 70F-75F (21C-24C). If the room temperature is 68F (20C) or less, the dough will not rise. In winter time, when my place is at around 68F, I slightly prewarm the oven (just warm air inside) and put the flour inside for 30 minutes before preparation and warm the water a little. I also put the dough inside the over for rise (preheat once gently oven to have warm air, then keep the door closed).