Maybe Rainforest is on a good train of thought. Perhaps you could buy him a teddy that he can snuggle up to in your bed instead of snuggling up to mummy. Then he might start associating the teddy with comfort instead of just you and when you put him back in his own bed the teddy will be a mummy-substitute to some degree...

I've not been through the situation yet though (Kyson is only just over a month old and co-sleeping) so I have no idea if this plan would work I just hope that you find something that can help you both feel more comfortable at sleepy time Good luck!