Teketeke I'm sorry to hear of your troubles with your oven. I have an old but reliable oven and not wanting steam to damage it I use a large roasting tin to cover my bread at the beginning of the bake. There are grooves around the bottom and I add water to the outer groove and spray the sides and lid. As it is made of very thin material I do not preheat it. I find it safer to use without preheating too. Depending on what I am baking I generally remove the lid after about 15 minutes.
Khalid (MeBake) has posted photos of his set-up, he has even added a baking stone to the lid of his. Take a look:
Others use a stainless steel bowl (search on TFL using "Susan's magic bowl"), but for baguettes, something longer is needed. I hope you can find something suitable for your oven to cover your baguettes, to provide steamy conditions at the beginning of the bake.
Have you seen Shiao-Ping's post on the baguettes she made from the Mandarin translation of the bookバゲットの技術 ?
I am looking forward to shopping for bread baking books when I am next in Japan (and eating lots of yummy bread too!)