Firstly, I'm very glad to hear that declawing is not something you'd consider.
Ok, how to deal with cat and baby. What happened before the cat scratched your baby? Did the baby poke his eye, tug his tail or fur? Whap him on the head? All of the above reasons are valid reasons for the cat to tell your baby off. I don't like being hit on the head by a baby, but as an adult human I'm aware that the baby didn't do it to be mean...your cat is not aware of that and so he reacted as he would if anyone else hit him on the head (or whatever baby thing your kid did to cause a reaction like you described), defensively.
Cats can also react this way to loud noises, surprise (such as the baby rapidly moving towards him), and other startling things that happen nearby that have nothing to do with the baby.
I want to be clear that I'm not saying it's OK that your cat did this, but that is is something most cats would do. That doesn't mean that there's nothing you can do, but rather that you need to be aware of why this happened in order to prevent it.
You need to know what sort of actions can trigger this reaction from your cat so that you can prevent them, and now that you have a mobile little one it's crucial that you are always
there to redirect your baby for the safety of both of them.
Things you can do to prevent future scratches, supervise very closely and don't encourage your kid to interact with the cat. At all. IMO children shouldn't have anything to do with pets until they are old enough to fully understand how to be gentle. Period. it is not safe for your pet or your child if the kid is allowed to hit the cat as hard as he likes, even if a baby doesn't understand he is hurting the cat.
For me, this means that the only way you allow your child to interact with the cat is from afar. For example, sitting on the floor watching kitty play with a toy across the room. Or looking at the kitties fur from far away, ect. Yes, cats and babies are cute together, but babies and cats aren't known for their self control. Since your hubby has already given your cat an ultimatum I'd err on the side of caution.
When they have to be in the same room together you could encourage the cat to think of the baby as a good thing by tossing him treats to keep him at a distance. Eventually he'll learn that staying a good distance away result in goodies, and lots of petting from yourself of course.
Make sure your cat has a lot of places to go where the baby can't reach. On couches, tables, counters, windowsills, cat posts ect. Until your baby is old enough to learn some real self control the cat need to know he can escape if he needs to, and you need to encourage him to do so. I'm not saying act aggressively and chase your cat away from the baby, but I would gently discourage them from being within reach of each other for now.
The other thing you can do is make sure your cat isn't feeling left out. Babies take up a lot of time, energy, and attention...all of which your cat had more of before this small loud smelly being came into his house. Take some time out each day to play with the cat, pet him, and spend time with him. That will reduce the level of energy he has, which will hopefully mean he'll spend more time sleeping and less time following your mobile baby, and that he'll be generally happier and less stressed so if they do happen to interact he'll respond more positively.
Learn to watch the cat's body language for signs of stress; lashing his tail around, crouching, staring, putting his ear back, licking his lips, ect. if he's near the baby and showing any of these signs he's stressed and that means he's more likely to lash out.
Just because he wants to be near the baby doesn't mean he LIKES the baby. Babies have all sorts of strange smells on them, they usually have food nearby, and they make noises. All of those are reasons your cat could be nearby that would not always lead to good things between the two of them. He could very well be 'keeping his enemies closer' so to speak. Cats tend to follow around people or animals they are uncomfortable with, they don't want to leave them unsupervised in their territory but they don't want to get too close either.
the last thing I'd suggest is looking into trimming the cats nails more often. This way the cat still has it's claws, but is much less likely to hurt the baby. If you have a particularly calm cat who will let you handle him easily you could look into training him to accept a dremel, and use that tool to blunt each nail. Again, this is another way to prevent the cat from hurting the baby while still keeping it's claws.
To me the fact that he's jumping onto shoulders more often suggests that he's uncomfortable with the baby, now that he's mobile, and is looking for a way to escape as well as reassurance.
All of this is stop-gap solutions, because the fact is that your child will need to learn to properly interact with the cat at some point. When the baby is old enough to be gentle, follow instructions (with you RIGHT there), and show some self-control then you can work more on getting them to interact nicely...but for now teaching them both how to avoid each other is where I would start.