When to move to a grown up bed?

[LittleMonster100]

Dc1 is currently 17 months and will be 21 months when dc2 is born.

Dc1 is currently in a cot, but is on the 99th centile for height and ver tall, so seems like the cot won't last very long.

We live in a rent house and can't fix a stair gate t the top of the stairs - it's an awkward Victorian staircase and the shape won't allow for a stairgate.

Dc1's room is right next to the stairs, open the doors and steep stairs are right there.

Worried about the cot not fitting when dc2 comes along (who will be in our room) and having to get a bed and dc1 walking out and falling down stairs.

Any advice?

[Sirzy]

Can you put a stairgate on his bedroom door?