Hi laumiere. That's great! 32 hours 1:1 means basically, all contact time. In other words, from 8.50am-3.15pm each day. So, what you need to identify is why he needs that support, and then get the relevant professional to state it.
We are one step ahead of you, in that the LA have agreed to assess.
DD is a bit of a tricky fish, and needs 1:1 for a variety of reasons. So, we so far have Portage Outreach, who say 1:1 for communication and safety (DD is a 'runner' but also unsteady on her feet); Occupational Therapy, who will say (I think, haven't seen report yet) 1:1 due to safety, and sensory processing, plus communication; SALT who have just scored DD as on 5th centile for understanding, so 1:1 for differentiation of curriculum.
So, if your DS needs 1:1 for physical reasons, you need support from the Paed, or Physio, or his current setting. Language issues would be his SALT, etc.
If the LA agree to assess, they will write to all the people involved in your DS's care anyway, and they will each give their recommendation. Also, you will be asked for your views.
Be sure of what your 'line' is. Ours is that DD gets 32 hours 1:1, or she doesn't go mainstream. Full stop, no negotiation. She HAS to have 32 hours or we can't even consider mainstream. Mainstream is cheaper than special, so we have that on our side.