Hi N.,
I know you were probably hoping to hear from moms with kids in toddler beds, but maybe I can be a little help anyhow. :-)
I have a GREAT sleeper who is 2 years old. Thankfully he hasn't started climbing out of his crib yet, so he still sleeps great there. I think he feels safe there. (If you think your son might feel intimidated or just want to be cozier, IKEA makes little bed tents that would probably make him feel less vulnerable. A bed so close to the floor is an awfully long way from the ceiling - maybe it's just a strange sensation of suddenly feeling too little in a big room.) Despite all this, he has an occasional seemingly sleepless night, too.
He had a rough time when he transitioned to 2 hour naps, too. In fact, sometimes at his daycare (which was new to him at 15 months old), he would nap only 30 - 45 minutes at a time! Of course, he was overtired and didn't sleep well at night, either. We always woke him up at 6:30 (and still do) because hubby and I both work.
When he wasn't sleeping well at school, we watched for signs of sleepiness way before his normal bedtime at 8:00 PM. If he was getting cranky, rubbing eyes, staring off into space, looking loopy, stumbling around, getting frustrated more easily than normal, etc., we headed off to bed early. We also have a strict bedtime routine that we follow every night no matter where we are. Bath, brush teeth, PJ's, Bible Story, Goodnight Moon (which we can recite by heart now), lights off and 2-3 minutes of prayer while snuggling, then we sing the same soothing song every night. After this, he's had a few minutes to adjust to the dark and we give hugs and kisses to Daddy, Mommy, and Brother and we put him in bed by the night light in his room. By the time we get to turning the lights out, he's yawning and usually goes right to sleep. He likes to be nice and toasty (like me) when he sleeps, so he wants to be under a light comforter. You might consider if your little one is comfortable, too. Are PJ toes too tight? Diapers too snug? Blankets too heavy or too light?
There have been times in the past couple of months when he'll stand up in his crib and ask for water. Usually I take it in without a word, touch him soothingly while he drinks it and he goes right back to bed (I do "tuck him in" by covering him up again). If he resists, I tell him it's "night nights" and that I'll see him in the morning. I then leave the room and don't go back in. He settles on down pretty well. You might try this as he may be getting less to drink during the day than he's used to. If he's not verbalizing that he's thirsty, it's hard to catch this one. (My little man used sign language at first to tell me he was thirsty, so I caught it quickly.) I don't know about you, but if I'm thirsty at night, I'm getting out of bed and heading for the sink.
I also recently noticed that his second molars were starting to come in. He's never been one to complain about teething, but he did get a bit fussy just before they broke through. Combined with a rough napping day, it was sometimes hard to settle him. On those nights I would give him Tylenol before bath or brushing teeth and by the time he got in bed, it started kicking in. Whether he's teething or not, sometimes Tylenol helps my little ones get a little more comfortable before going to bed if they've had an especially long or trying day.
I'd also be sure to encourage him and praise him for good nights, and maybe even preparing him verbally a few times before he climbs into bed will help. We've done similar things with my 2 year old such as, "In a few minutes we're going to go play in the bath tub!" and then "Almost time to climb the stairs to go get a bath!" Then when it's time to go, we ask, "Micah, would you like to come upstairs with Mommy and Daddy to help give Elijah his bath?" Usually he can't wait to go. And we make a big deal out of leaving his shoes on in the car or behaving well when we go places. He seems to like pleasing us, so maybe similar things will help you.
Hopefully my rambling has been a bit helpful. :-) Above all else, know that this is most likely a phase and he will grow out of it eventually. I've never known a teenager who can't sleep a good 15 hours at a stretch. ;-)
I have heard that toddlers take steps backwards in some areas when they reach new milestones, so this could be the case, too. Just keep up a routine, check for comfort and thirst, use your best judgment about whether he's fussy or truly needs something, and in time he'll be sleeping like a champ again.
In the meantime, Hang in there!!
Smiles,
L.