So, I am a deaf studies/interpreting/communications major, and I focus on linguistics, specifically literacy and language acquisition. (I'm hearing, if you care.)

I have done some studies/papers on teaching sign language to pre-lingually and post-lingually developed children, and the research is overwhelmingly in favor of teaching sign language pre-lingually.

Think of it this way: When you teach your child sign language, you give him a visually based language system that is attainable for him. You are providing a source of language that follows syntactic, phonological rules, which will help him learn an auditory language so much easier because he will be able to relate it to something both in his original language (whichever signed language you choose-- I assume USA, so ASL), and physical, contextual components can be added for more reinforcement.

Also, do you have any "hearing impaired" programs around you? Near me, a few schools do things like have special microphones to use if a student has a hearing aid, some teachers use total communication (talking and signing at the same time), and other resources to make education completely accessible.

As long as you work towards learning ASL so you make communication as fluid and accessible to your son as you can, that is what matters.

This part below may be overwhelming to read now. It's about literacy acquisition! Since your son is very young, it may be better to save to read later :)

Also, here's a little tip that may help him later in life that I found when I delved into my articles: many studies have shown that deaf/HoH kids, when learning to read and write, do not make the connection between a signed letter being the letter on the page. They don't have the phonemic reinforcement to make the connection. So, say you're teaching him the word ball in a picture book. You would sign him the word ball and point to the ball on the page. Then, fingerspell the word ball and point to the word on the page. Then, fingerspell ball as the individual letters, and as you do, point to the graphemes on the page, so he knows that each letter is represented by the sign.