Most convertible seats start with a really low weight, like 5-8 lbs, so you would be okay to transfer to it, rear facing. The convertible sits up more than a bucket seat so that could help. Or if you aren't ready to purchase the next seat just yet, maybe try putting him in there for a little bit in the house where he can see you so he gets used to the seat?
My sister had a mirror for her DS. I don't know that he could see her with it, but he was entertained looking at himself.
My kids both went through phases where they cried all the time in the car. With DD, I used to have to sing the entire way to and from places (which were sometimes over an hour away) to keep her happy. Then she finally got used to a lullaby CD and we listened to that everywhere we went. I started earlier with the CD with DS so that usually worked for us.