OP it is simply dreadful and I don't know what the answer is. I do however want to point something out. If children can indeed spread the virus easily, then they won't just spread it to a teacher. They will also spread it to classmates. Children are not social distancing at all in schools (teachers are in our schools). So I have 3 DC in 3 different schools. One is in a bubble of 30, one is in a bubble of 25 and the other is in a bubble of 120 and she is doing GCSEs. Therefore as a family, we are exposed to all of these children and teachers.
I see around 50 patients a week (up close and personal), often in their homes with their family around. My DH is in the police and also up close and personal with many people.
Like most families, our exposure is high. Remember, our masks aren't protecting us, they are protecting the people we are close to. We are all in the same boat is my point, not just teachers.
If PPE would make you feel better then you simply wear it or tell your head you will be going off with stress (as you do sound incredibly stressed, understandably).
As for testing, of course it is a disgrace, we know this. Again, not just teachers in this boat. It is a massive problem for everyone. You are lucky in that you will be getting full pay whilst isolating, many won't. You will be off anyway as you say you are literally too ill to expand on your posts so clearly you would be sick off anyway even with a negative result.
I really hope that you fell better soon 