I'm sorry things haven't worked out the way you hoped, OP.
Your little boy sounds lovely and you obviously want the best for him.
I work in a secondary school.in France and have done for 30 years. The system is quite different but there are similaities.
I have noticed that the number of children with additional needs has increased enormously over that time. In my current school, which is in a leafy, affluent area, up to one third of the children in some classes now have some sort of 'plan' in place, usually involving adaptations for things such as dyslexia, adhd and so on.
I will say up front that France is not great with this (understatement) and can massively improve.
However I do believe some children are just not being taught resilience by their parents. I also believe that this is behind some of the mental health problems we see among teenagers.
Some parents expect us to provide the same level of nurturing care in a class environment as they provide at home. We're asked to tale into account the most bizarre requests sometimes (Marine needs to be able to do all her tests on blue paper because this colour calms her. Achille's psy says he must not be marked down if he doesn't answer the precise question as he can only perform well when he feels free to express himself freely. Rigid structure [essay question and expected format] makes him feel anxious).
It's just not possible, and I don't believe it is beneficial for the child in the long run. They need to learn how to rub along with others, how to develop a thicker skin, that not everyone thinks or behaves the way they do, that their every whim and desire cannot be satisfied. That sometimes we need to do things we find challenging or unintetesting. That we won't always get top marks.
We do our best to prevent and deal with bullying but it does unfortunately happen. Sadly, ND children are targeted more than others.
I'm rambling now. But this is to say that we can't protect our children from everything, however much we might like to. In my experience, facing a little adversity often allows children to exceed expectations, and allows them to develop more self-confidence than shielding them does.
I hope you find a solution that works for your family, in the long run. It might be that one of the local state schools you have discounted will allow your son to thrive, as long as you prepare and support him.
The best thing you can offer all of your children is a solid, happy marriage as the foundation of your family which gives them the confidence to go out and face the world.
I am not convinced that taking on a second job or burdening yourself with financial stress is a good way to achieve this.