The Montessori bed is characterized by being flush with the floor. In this way the child can access and descend with total independence.
From what age can they sleep in a Montessori bed? I will not tire of repeating that each child is different. If they dare, they can start using the beds at an early age and only for naps. And to feel completely comfortable, they can reinforce security by surrounding the mattress with cushions. In case the baby turns and falls, the pillows can amortize the fall.
As the child grows, they can adapt the bed to their needs, but without ceasing to respect the first rule: that they can access and get out of bed on their own.