sleeping on front and moving to bed

[fi123]

ok,. my son is a large 21 months. i have all junior bed stuff ready but not sure what to do. He sleeps fine in cot and naps etc, but he sleeps on his front and goes all over the cot, even stuffs himself in the corner (which looks uncomnfortable). Will he be ok in a toddler bed as he sleeps like this? my ast son didnt and was fone at 23 months in a bed. help?

dd went into a full size bed and was fine - I was worried about her wriggling. We put her cot mattress on the floor so she would land on it and not the floor - one time I found she'd fallen out of bed and was asleep on the mattress on the floor!