I'm a fan of loft beds (top bunk with no bottom bunk) to allow the space underneath to be used. Six of my children (and myself) have them, with the second youngest receiving hers for her 3rd birthday - though hers is only 135cm, the others are 165cm high.
My baby is only 2yo and she isn't allowed in her sisters beds. Occasionally she decides she want to - likely because they've encouraged her - but we all have to be stern with her and she stops.
However, since heat rises and it is quite hot at the moment, Miss16 has been sleeping on a foam mattress on her bedroom floor, as it is too hot in her bed.