M., Place rolled up blankets on either side of him, so that when he does wake in the night, it seems like he is in his crib. Extra space around a child feels odd, and can even frighten them, because they temporarily don't know where they are, and it may be slightly colder. Also, my son goes to sleep with a sleepytime lullaby CD, so quietly that he just barely can hear it. If he wakes in the night, I go in and see what's the matter, and then give hugs and kisses, and then turn on the music again. He relaxes, and it puts him right back to sleep. You can even record yourself singing, if that helps. Also, my son has a "lovey,"....some kind of stuffed animal, tiny. His is a little lamb about 5 inches long. When he was as young as your's, he had one of those little square foot blankies, with a stuffed dog, cat, animal sewn into one corner. Just small enough to hug and cuddle, not large enough to hurt while sleeping. Also, our son has one of those tiny lights that plugs into the outlet and only comes on when there is some movement in the room. It is tiny, and then after no movement for a while, it goes back off. So, it is not a distraction, but rather a reminder of where he is, and that gives him comfort.
The only other thing I can think of is that he may not be ready for the toddler bed? You would know better about that. We didn't transition, until our son was trying to crawl over the railing of his crib. But since Cooper is already in the toddler bed, I don't know that you would want to switch back again. Anyway, I wish you all the luck in the world.
J.