O.C.
I think 1 1/2 is way to young to put him in a toddler bed. You should really try and keep him in his crib as long as possible. 2 1/2 is a good age to try and start the transition from crib to bed. A good idea when that time comes around is to keep the crib in the room and then bring in the other bed in. You can slowly read him books and help him fall asleep and play in the bed which will slowly let him get used to it. Once he's ready you'll know. As far as what bed to buy. Ikea sell great cheap toddler bed that are fun and fashionable. They also sell other great beds that are close to the ground. So, if you wanted to skip the toddler and go right for a twin, height off the g round would be a non-issue............ The longer you can keep him in the crib the better. You don't want him wandering around at night etc...... if he crawls out (like my daughter did at 10 months old. buy a crib tent. It's like their own fort.