I haven't been there, but here are my thoughts:
Try talking to your 4 year old. Tell him that you really need his help to keep this new baby safe. (I've never known a child who didn't adore the new baby) Tell him that you just can't have so many people in the big bed while the new baby is getting used to being outside Mommy's tummy, or even that he is too big and moves too much and might accidentally hurt baby in his sleep. Anyway, most 4 year olds want to help, so tell him that his way of helping is to be a big boy and sleep in his own space. Whether you tell him not to come to your room at all, tell him to come get you and you will go back and tuck him into his own bed, or make him a small bed beside yours, just make sure that he understands where he is supposed to be. Then, in case he really does just need the snuggle time, in the mornings he can get in bed with you and the baby and snuggle for a while before time to get up.
Try to talk about what a big boy and a big helper he is, and how important it is for the new baby to be as safe and happy as he is.
Proud Army wife and Momma of two.
Jay-my precious boy 2/20/08 & Caroline-my beautiful HBAC baby 8/22/09 :