Switching To Big Bed

"Hi, I'm Bianca. I have a 2 year old son, and am 12 weeks pregnant with our second child. We are currently trying to decide if our 2 yo should move into a big bed. He is very tall for his age, so could use the extra space, but has thus far shown no desire to leave his crib. On the contrary, he will sleep nowhere but his crib. He does not try to climb out of it and sleeps across the top, liking the feeling of security. We would like him to be in his new bed, whatever bed that may be, within the next couple of months, so there is no jealousy of the baby. We just aren't sure if we should buy a crib that converts into a toddler bed, a toddler bed that converts into a big bed, or just go straight big bed. What do people think?"