ASD Unit in mainstream school or Special school

Hello All,
First of all thanks to anyone who takes the time to read this. I have a little boy who is about to turn 3 and was recently diagnosed as being autistic. He has been attending nursery sessions at a brilliant special school since late last year. At his review they indicated that long term the school he is at (which we love) would not be a suitable option for him and he will likely change schools in a year. I asked what they thought might be suitable and they said a mainstream school with an ASD unit attached. I suggested perhaps a school that is solely for ASD pupils but they didn't seem to think so although they didn't say why & I will be asking after half term. They are starting his statementing process and are confident that will go through fine. 

So here's my dilemma. I am extremely concerned about sending my boy to a school that is predominantly mainstream. My main worry is that he will be bullied or teased and won't even realise or be able to tell anyone. He has no comprehension of others emotions at all and just thinks everyone wants to play with him. As he gets older the difference between him and other 'normal' children becomes more pronounced. His peer group now comment on his lack of speech (he only has limited single words) and not always in a very nice way. He is also a master copycat and because he wants to play with anybody around but doesn't really understand how that normally works he mimics other children. This can be irritating to them and has led to some unpleasant experiences where i have had to remove him when the children get annoyed with him. He also likes to be affectionate and hug other children but frequently tries to do this to children who are not actually being nice to him. I know it sounds small but he is very long sighted and has to wear glasses with very magnifying lenses which sets him apart from most other children and can make him a target for mean kids. I really don't know what his best options are and I didn't think he would have to change schools so soon. The school he is at now is so lovely and he thrives there but I guess they will need the space perhaps for a more disabled child. All of this is causing me a lot of anxiety. I can't raise it with his teacher until after half term so I was wanting to hear the experiences of others.

The nearest ASD school is about half an hour from me and is very good. There are also two small ASD units attached to mainstream primary schools near me. One is at a very bad school and the other is at a good school but they only take children up to age 7 anyway. I really want to hear any experiences, good or bad,or advice about my options. In the end will I even have a choice or if his teachers think ASD unit in mainstream is best is that what we have to accept?

Thanks