I'm glad you do plan to go to a toddler bed. Do it today. Picture this: Look at the top rail of the raised crib side. Look at the distance from there to the floor. Picture your child falling that distance -- head first. Keeping climbers in cribs is asking for injury or worse; my friend's child broke her arm at 18 months the very FIRST time she tried to climb out of her crib.
I know you don't want to hear this, but here it is: You will have to go through another sleep transition with the toddler bed and a gate on the door won't be enough to handle it. He has to be taught that when he gets out of the bed, and he will, that he gets no "reward": No attention, no talking, no playing, just right back to bed.
When he gets up, you quietly say, "Nighttime is time to be in bed," then walk him back to his bed with your hand on his shoulder. Do not fuss at him, don't scold, do not engage him in any further talk, sit him down, lay him down and leave. He will do it again; you don't talk the second time but walk him back. It may take MANY times for some nights to come but it's the only way he learns that getting up gets him zero attention and zero excitement. The gate works for some kids but won't teach him to get back into bed; it will just let him roam his room unless you also go in and walk him silently and firmly to bed. Not a fun period but one all toddlers go through.
It helped us a lot that the first week I stayed in the room but in silence and in the dark, until my daughter was asleep. Then for a few more weeks I stayed where she could see me just outside her cracked-open bedroom door (I sat and read in the hallway--nice reading time!). Then iin later weeks I just checked on her after 10 minutes, then after 20 more, then after 30 more. She always knew I was there and she felt secure and eventually would go to sleep without my having to be within view or nearby and did very well after that.