A.A.
If he's not lactose intolerant, a little warm milk will provide a bit of tryptophan which causes drowsiness in a lot of people. Making sure he gets 10 minutes of sunlight a day to make sure he has vitamin D to work with in his system is also a good idea for regulation. If those aren't enough, the meletonin might be worth a try. Some people respond well to quiet instrumental music as well.
As for staying in his bed, some children just have higher levels of anxiety than others. It may just be that he really will need to share a bed with you for a few years longer than his siblings did. For a few children, returning to his room with him when he comes for you in the night, might get them a little more comfortable in their own space, having more positive associations with it. But obviously that won't work for everyone and get's old fast if you want to be in bed with your spouse.
One thing to watch for is if there seems to be any unusual sleep patterns like gasping in his sleep or pauses between breaths and such. A few children manifest early sleep disorders that will just make it hard for the reptile parts of the human brain to trust that sleep isn't dangerous. So they will tend to be light and fitful sleepers.
If all that pans out to nothing that helps, you may just have to be patient a while longer with this one and keep trying the prizes for success and such. Some children are more motivated by special time together, or other forms of love than gifts, too, or you just might not have the right gifts for him.
Keep experimenting.