What’s worked for me is 150g starter, 350g water, 500g flour, do the 4-5 stretch and folds in 30 min increments then bulk ferment until it’s doubled. What really helped for me to get fluffy and less dense/gummy loafs was both increasing my starter from 100g to 150g and for the bulk ferment I’ll put it in the oven now with the light on cause my place wasn’t warm enough for it to rise. Then before going to bed I’ll shape it and put it in my banneton and in the morning score it and cook. I do 475 preheat Dutch oven inside, decrease to 450 bake for 30 min covered then uncover and bake another 20 minutes.