Mini Crib?

Baby will be sharing a room with his/her big sister, who will be just about to turn 4 when he/she is born. I imagine the baby will be in our room for some months but my daughter started sleeping through the night at 6 weeks so we put her in her own room then and I want to be prepared with a crib of some kind in case that happens again (unlikely, I know, we were lucky enough to have it happen once, but just in case). The room is odd shaped so I don't know that a twin bed, a regular crib, and a dresser will all fit in well. Has anyone used a mini crib? Has the baby outgrown it quickly? I want the baby to be able to fit in the crib for about a year and a half before we transition to toddler bed and I don't want there to be an issue at some point of baby being too bit for the mini crib but not yet ready for a toddler bed. I also thought a mini crib would work well in our room instead of a bassinet if we decide to go that route before moving him/her in with big sister. 

Any thoughts or experienced that would make us reconsider a mini crib?