I was pregnant with my daughter by my sons first birthday. So we needed to switch him rooms. She was going to need the crib and I did not want to buy another one or get a toddler bed. So we bought a mattress and box spring put them on the floor with a bed rail. We decorated his new room with all kinds of sport balls, didnt let him see it till it was finished.
This was when he was 16 months. I didnt want him to feel pushed into his new room when the baby got there so I made the transition while I was still pregnant. 3 days and he was sleeping all through the night in his bed. The first night he woke up and asked to go back to the crib. He started his nap in his crib and after falling asleep I would move him to the new room. The second night he slept in the crib then the whole 3rd we played in his room. I laid on the bed with him played with his new balls and said he should take a nap in there. He did, it was a shorter one, So we played hard that day. Put him to bed very tired and didnt hear a sound till he called for me in the morning.
We put a baby gate in front of his room so he couldn't wander if he wanted to. He was told to stay in bed and sleep then call for mommy when he got up. He never wandered, he continued to sleep in his big boy bed even after sister arrived. We have had no problems even now that he is 5. He has never gotten into anything. When he wake up now he comes to our room and asks to watch tv or if he can turn on his light in his room.
You need to be firm. You need to be consistent. You need to make it a fun thing not a scary one. If mom is scared or worried then they will pick up on it. If your not ready they will not be ready.
If you want to hear how my daughter did email me. I would be happy to tell you.