I learned a trick from another site that really made the transition easier. I nested my daughter.
You will need: a crib wedge, a knit crib sheet and a couple of beach towels.
On top of the bare mattress, place the crib wedge at the top of the crib.
Take the 2 towels and lay one on top of the other (to make them thicker). Roll the towels, the long way to create a very long hot dog.
Place the hot dog in a horseshoe shape where the crib wedge ends.
Put the knit crib sheet over the whole thing.
Now your son will be a little cozier in the crib. Place him down so that his armpits on up are on the wedge and the lower half of him is in the nest. You can adjust the towels (through the sheet, usually) to make them wider or more narrow so that your son is cozy, but not claustrophobic. :)
This made the transition to the crib pretty seamless for my daughter when she was about 3 months old. I had first tried to have her take naps in the crib, but eventually found that didn't work. One night, when she had had a nice day and was pretty drowsy, but not asleep yet, I just decided "tonight's the night" and put her in the crib. She was a happy camper and we never went back to the bassinet. HTH Good Luck!