I’m trying to not use summons of the bosses of the dlc. At least for the first playtrought
I did the same, had +20 blessing but otherwise no summons or ashes. Still took four hours of grinding before I got the run. I did use a black steel shield +4 which negates holy damage, though you can still run out of stamina. Tough fight.
I think I’m still at +17 blessing and I thought e explored a lot. As far as I know I missed no area or boss