I think everyone who has responded to your post has good ideas. Five is old enough to be able to have a discussion with your son about where he should be sleeping. I would explain to him that his bed is where he needs to sleep. Consider allowing him to come into your bed for Saturday morning snuggles, so that he doesn't feel like he's being completely rejected. Put a clock in his room so that he knows what time it is (When you see a 6 on the clock in this position, you can come into mama's bed if it's Saturday) My parents used to let us snuggle with them on Saturdays when it was "light outside" which is another option.
Make sure he has a stuffed animal, or even take him to the store to buy one he really likes (or a body pillow) and tell him that when he's feeling lonely in his bed, he can hug the stuffed animal or pillow and it will be "just like being in bed with mama" not true, but hey, maybe it will work.
Tell your son about the new rules, the reason for the rules(you need sleep to be a good mama and he needs sleep to feel rested and happy), and that he will need to stick to them.
Start enforcing the new rules, whatever you set them to be, on a Saturday (so he gets the snuggle time if you decide that works for you) and make your husband the enforcer of the rules. If he comes into bed, he needs to be put back without any talking or stimulation over and over until he gets it. It's key not to show him frustration or give him any attention aside from telling him that he's to stay in his own bed until morning. This could take a while, and you might be exhausted while you go through the process, but a couple of weeks of sleeplessness for years of peace and quiet seems a fair trade in the long run.
When he stays in bed for the night praise him and tell him what a big boy he is. But, you don't really need to "punish" him if he doesn't, just let him know who's boss and put him back in bed. I would stay away from bribery because even though it can be effective, eventually kids get the picture that if they act out and then behave they'll get something. So, that can start a pattern. In my opinion, they should follow rules because they're rules and get rewarded with lots of kisses and hugs and positive praise, not toys. But, that's what works for my family.
good luck!