Cot to bed transition - 2 yo won't go to sleep

[Lostboys16]

I've had to take my 2 yo (March birthday) out of his cot as he had learnt to climb the sides and was throwing himself over and onto the floor (no fear!) He's now in a low Montessori-style floor bed but bedtimes have turned into a nightmare.

He won't settle, is up out of bed as soon as we leave, opens the door, leaves his room, cries for water, pulls things out of drawers and wardrobes to play with, makes an unacceptable amount of noise (I have an older child asleep in the next room). This can go on for 3 hours no matter how many times we put him back to bed. Other than changing beds, I haven't done anything different with his bedtime routine (milk, teeth, story etc.)

All tips online seem to be about being firm, putting back to bed without speaking etc. but it doesn't seem to be having any effect!

He has a speech delay and can't communicate with words yet though he does understand everything we say to him. Would be grateful for any advice from anyone who's dealt with similar?

Stairgate on the door. You get extra tall ones, I think they’re advertised for dogs 🤣 but they also work for climbing toddlers. Strip the room of anything he can cause trouble with and/or baby proofing locks on the wardrobe maybe. Then leave him a few quiet toys and books plus a no spill sippy cup of water and leave him to it unless he’s really upset. If you go into for the montessori thing they’re supposed to decide to go to sleep for themselves hence the floorbed. And IME they potter about a bit, get bored, realise they’re not getting attention and genuinely do put themselves to bed. I’m sure it doesn’t for every child but it’s certainly worth a try.