In general I would not just change schools, because the same thing would likely be the case in another school.
I think he's probably describing the issue accurately. It's noisy, too much going on, too chaotic. They aren't bothered at the school because that is what almost all schools are like and they think it's normal. (It shouldn't be, it is stressful and horrible for many children.)
FWIW - this was me at school. I loved the first day, I hated it after that. It was just too overwhelming. Mostly the teacher thought I was fine but I didn't like it there and it coloured my feelings about school right up into my teenage years.
The only exception, for me, was the second year. My teacher after my first year suggested I repeat - my parents, who thought I was bright, were shocked, and took me for an assessment, where it was suggested I could be moved to a better setting, skipped with supports, or repeat with supports. My parents moved me to a private school to repeat - it was a class of ten and half days, and I loved it. We actually covered more school material. Unfortunately they couldn't afford to keep me there after that year.
If you can find a quiet little school OP, I would try that. Or, just keep him home an extra year. Kids with ASD are often developmentally behind in terms of emotional maturity and he could very well benefit from just waiting a year to start into a big classroom. It could also be good when he gets to the teenage years as he is also likely to lag a bit socially behind his peers at that point which can lead to other issues.
As far as 1:1, my instinct is that it isn't going to address the actual issues that your son is describing.