We moved DD out of her cot into her bed at 17mths to prepare for the impending arrival of DS.

I invested in a portable bed side from KMart which has two fork-lift type prongs which slide under the mattress, and a mesh bed side which sticks up about 30 cms and stops toddlers from rolling out.

It packs away really small, so it's easy to take away with us (DS now uses it when we go away).

Best $20 I ever spent.