New to posting here!
I've been trying my hand at freeform bread for a while, and wasn't having much luck with oven spring. After producing some edible frisbees resulting from overproofing, I was still having difficulty, even with oven stones. Reason: I refuse to preheat the oven for an hour, as I just can't justify that energy use to myself. So the stones were really not hot enough.
But I found a great alternative! We had a small iron BBQ hotplate that fits into the oven and it works like a charm. It heats to the temperature the bread seems to need, in the time it takes for the oven to get to the required temperature. Like all BBQ plates, it's slightly concave in the middle, and it has a small drainage hole for the fat - but neither of those things makes any difference to the bread when I cook it. It's ju-u-ust big enough to take a 2kg miche (as long as I'm a dab hand getting it off the peel and into the right place), and the miche cooks all the way through with no dramas, great oven spring and a good crust.
Might help someone else out there.