[SaraElise]

If it's a space issue I would just go straight to a twin and skip the toddler bed, it's the same size without crib rails.

As far as when to do it, I'd probably wait until it was an issue. For me that meant 17, 18 and 13 months for my kids to climb out/hate their cribs. All 3 transitioned fine with maybe 1-2 hard days. Even naps were not a problem.