With the SA, do you think it would help if, once you have made a decision about what you will do, you talk to him about what will be happening? I know he might not respond but you never know what they take in!!!
My LO is due to move up but I was concerned as she has only just changed carers and we went through a month or so of SA, terrible crying when dropping her off and her not even wanting to go through the door to her room but I spoke to a couple of mum friends and they told me to talk to her about it at home, which I have been doing.
Also, I guess whether you move nursery or move him to the next room, he will react the same way so is it possible to arrange to have a/some settling in session/s? We are allowed to make appts where we attend the new room with LO for an hour or so. When we first started, we had about 3 sessions booked, I attended the first one then only stayed for part of the next one. At the last session, I just dropped her off and picked her up again an hour or so later. We've got a session booked next week to go to her new room together for an hour.
Also, I don't know where you are based but in the UK, I believe most nurseries are Ofsted registered and comply with the Early Start programme. Every so often, I receive little reports telling me what the aims are and what has been done to achieve it. E.g. one term, they were learning about making noises so they had play sessions with musical insrtuments - we get photos of them playing!
Do you get anything like this?