We had the same situation with our daughter, except we made the transition at 4 1/2 months instead of 6. I worried about it a lot more than I should have. We first started with the sleeping in the crib at bedtime....she would usually fall asleep with her last feeding, and I would lay her down, and she would stay asleep...now I try to put her in there while she is drowsy but still awake, so that she will learn to soothe herself to sleep. After a week of sleeping there at night, we tried the nap times. It took a few days of reinforcing that she needed to sleep there before she figured it out. Now she is in the crib for all sleeping activities. At first, she would wake up once a night, but eventually she started sleeping through the night again. It really wasn't as bad as I had pictured it in my head. Good luck.
J. W