Can you go into his room when he is asleep and say " Honey, its just Mummy, I'm checking to see if you're ok. Sleep well Darling, I'll see you in the morning" to let him know that you are keeping an eye on him and he doesn't need to wake up to check on you?

I don't know if it works, but I'm trying it with my DD after my MCHN suggested it (she's fabbo BTW - a real do whatever works for you nurse).

DD is a little like your LO but we've turned a spare room into a safe playroom & put a mattress on the floor so when she wakes at the ungodly hour of 4.30am, we all go in there, we doze, she plays and when she is ready for sleep, she starts whinging and I grab her and pull her into bed. It works for us.

Hope you get some sleep!