Sorta off the topic, but my aunty is having her second mid to late september, and her first is 18 months old atm. What they were planning was to get her used to her big bed (ordinary single) at least a month before her sister arrives. As she'll be at the age of attachment to things. They also just bought a new carseat for #2 and my cousin will stay in hers.
Ill be doing the same with the bed when Chelsea is around that age cos bub will need her cot....unless bub gets to big for the cradle super fast then ill have to re think the plan!