transition to crib

Ideas on how to get my LO to start sleeping through the night in his crib??? He has been in his rock and play since 2 mos and think he just loves that feeling of being tight and cozy in there.  He will sleep i his crib for a few hours then wakes. Try letting him cry it out but at 2:00-3:00 am it's not really pleasant especially with another child in the house. 
Thank you!!!