Cot to bed transitioning

We put a rolled up (lengthways) towel under the fitted sheet on the non-wall side, I've heard pool noodles also work well. It seems to just give them enough feedback that they're getting to the edge. We also had a stair gate on his bedroom door frame so he couldn't get up to very much mischief if he got out of bed.

DS1 climbed out at 2y and a few days.
He was in a toddler bed from that night, and regularly fell out for about a year. He had a "crash mat" of a spare double duvet on the floor.
He still, 10 years later, sleeps in weird and wonderful positions, often across the bed, but hasnt fallen out afaik....
DS2 climbed out at 18 months. Into a toddler bed. Fell out about twice and now sleeps still enough for a cat to curl up next to his feet.

DS1 we moved at 2yrs 10m, DS2 we moved at 2yrs 4m. I kept them in a cot as long as was possible!

Is it really high that he’d hurt himself? DS is 12 months old and we cosleep for part of the night. He once managed to climb over his dad in his sleep and fall face first onto the carpet without waking up as our bed isn’t high. So if it’s low I’d probably just let him fall with a duvet or matt to cushion the blow