Hugs- it is scary to have a spirited toddler up out of bed in the middle of the night! I think I would do the following:
-do major safety check of his room, so if he does get up in the night, there's no danger to him- outlets, shelving secured, windows safety latched, etc etc.
-use mattress on the floor until the new bed is in place.
-talk with him about his "NEW" bed and how he sleeps in "his special big boy bed"
-curb any snuggles in your bed at other times in the day/evening until it's well established at night that he ONLY sleeps in his bed.
-as soon as he comes into your room, you must be lovingly firm that he sleeps in his bed. Return him to his bed EVERY time, even though you're half asleep! Better yet, get DH to help do it while you sleep/rest.
consistency is the key- and it should get better faster if you don't give in- Hugs, courage, and wisdom!!