B.G.
He's fine. This is just so normal. At this age their imaginations are working overtime, and they are learning so much. Being alone to fall asleep can be scary. It will pass. Just remind him that he is safe and that Mommy and Daddy are there if he needs you. If coming into your bed doesn't disturb your sleep, don't worry about it. Again, he's fine.
I doubt sleeping in a toddler bed is really effecting him. We skipped the toddler bed altogether. Our oldest had a twin bed from the time he was 16 months. Our youngest is in a full, but that's because we bought a twin over full bunkbed and he has slept on the bottom bunk since he was about 18 months.
He's fine. If you want to change his bed and he seems ok with it, go for it. If he's nervous, just wait. I think he'll be just fine either way.