If you are at all uncomfortable with the idea of getting married early next year, you could still become engaged immediately and simply allow more time before the actual ceremony. This would give you more time to assess the quality of the relationship and may also increase your level of comfort with the decision. I believe that it is normal to be somewhat nervous about getting married, even when you are quite certain that you have made the right decision. The commitment is one of the most significant decisions that we can make in our lifetime. In your case, though, you are going into it with some knowledge of what is required to make a relationship work.
Marriage does represent risk for anyone.
But, if you are certain of your love for this man and of his love for you and your child, formally committing to the relationship may be a risk worth taking. We cannot predict our future, but if your choice is between living your life with a man that you dearly love and living your life without him, I would suggest that the choice is a relatively easy one. Give yourself and your boyfriend the benefit of having enough time to get to know one another while engaged, and then, when you are ready, go ahead and make the formal commitment. Finding someone to love who is capable of loving you in return is still somewhat of a rare occurrence in one's life. If you have been given this gift, then by all means, let yourself accept it.