i had to do major tough love when my DS did this and we had to put gates in his door way. we made a sleep chart that we implemented (this was suggestion by his preschool teacher) and when he got out of bed we would not go into room but we would tell him "itime for bed" outside of the gates. the gates were clear and we stacked one on top of the other bc he either crawled over or crawled under. it was hard but we started on a friday night and by the next weekend he was STTN again. the first 2 nights were the hardest. the rest of the nights, we just had to say "time for bed" and he would go right back to sleep. i think i made my DH do the first 2 shifts over the weekend and i took over the rest of the week since i'm a SAHM. oh, and let me say i tried WIWO and GW and sleeping in his room and sleeping outside his room for WEEKS and i was so depressed. i mean i was sleeping on a mattress outside his room and he would still need assurance through the night that i was there! we were EXHAUSTED.
i have my almost 3 yo dd still in a crib w/ a crib tent on it and i am NOT looking forward to transitioning her to a BGB. i have no intention of doing it any time soon!!!
then when i got pregnant with my DD, DS started climbing into bed with us in the MOTN. I don't remember how/why this happened but he would sneak in on my DHs side who wouldn't take him back up. He said he was scared. anyway, he was much older than your LO and so we were able to use rewards, walkie talkies, and would check on him every few minutes as he was going to sleep. He was 4.5 though.
So, with my DS, we had to be pretty tough. and with my DD, who is having a bit of sleep issues right now, i am using the more tough approach. she wants us to stay in the room until she falls asleep but it takes her like an hour to fall asleep. if we just say its time for bed and leave the room, she cries for less than a minute and then falls asleep. BUT, she is in a crib with a crib tent so she can't crawl out.
you know your kid best and sometimes you have to try different approaches to see what works.