That is perfect bread and looks really tasty.
The whole point of the stone is that you must heat it for a long time. So you're not heating the oven, until the light goes out but heating the stone for as long as you can say 40 minutes to an hour after the oven has reached maximum heat. the stone draws moisture out of the base of the bread and caramelises the surface and crisps it. Also, use semolina in place of flour for the base of the bread if you can. That adds crispness. if you look at the bagels up thread there is a picture of a base of one . Because bagels are boiled they are wet and so I use semolina to absorb some of the water and add crispness.
Foil cooks bread in its own steam. It is pointless putting foil onto the stone. The stone won't be adding any value. So make yourself a peel or buy one they cost around £10 of amazon in the UK. Buy a wooden one not a steel one. Steel is cold and causes the dough to be more likely to stick whereas wood is warmer and pizza and bread is less likely to stick. A steel peel is better for removing the bread or pizza once it has cooked. Coat it with flour ensure the loaf is moving around by shaking it and then shake it off onto your very hot stone.
You'd also benefit from final shaping using the technique I mentioned earlier ie increasing top surface tension by balling the underneath into the middle. Look for a youtube on shaping pizza balls. So make a big pizza ball ... long in you like and cut the surface to release the surface tension and allow it to bloom. Also some more surface cuts, is stagger them inot a sort of zig zag. The bread is saying to me that it wanted to open more.
Have you yet become convinced at how a disproportionate amount of extra depth of flavour and character is given by using the starter? And how wonderful can such a cheap pastime be. Real men bake real bread!
I really like the inside of that loaf.

Thanks for all your help - this has been fun.

I'll get a peel next. Just one more question, if you don't mind...The bread was actually quite tasteless. The texture is spot-on, but it just doesn't taste like anything. Does this mean I need to use more salt when mixing flours with the poolish? I didn't measure it but used about a pinch of plain sea salt.
OK, two questions: how do you use semolina for just the bottom? You mean you sprinkle it on the peel and put the shaped dough onit before sliding into the oven?
I will look on Youtube for pizza dough shaping. It would be nice not to have bread that looks like an alien.
My fiance thinks I'm crazy for baking my own bread...well, not crazy but certainly eccentric.