My 2 year old is quite big and fearless for her age and has been adept at climbing out of her cot for a while, although rarely bothered. We decided the benefits outweighed the negatives, so extra baby proofed the room, left the cot sides on as a deterrent from climbing out and put a mattress next to her cot as a "fall mat".
All was ok until her baby sister started getting older and more fun to play with and now she has started climbing out of hers and into her sister's cot 
Guessing retrospectively from noises and the scene when we come in, they play nicely for a while then DD1 gets giddy and chases/catches DD2 and squashes her, making her cry and/or breathless which is risky 
We're really stuck as to what to do, we've caught her doing both manoeuvres and there's no step ups I can remove or ways to make it harder for her. She strips off to make it easier so using sleeping bags is no help either 
I would welcome any advice as to what to do please!