Hope you ignored the lady who tried to make you feel guilty for going back to work. It never ceases to amaze how others can judge so harshly - especially when they don't know anything about your situation.
Maybe I misread, but are you putting him into bed when he's already asleep? If so, that is part of the problem. I've done that and it's hard to stop, but it has to. They won't do that at daycare. At his age, it probably means putting up with some crying.
If that's not the case, then I really haven't any ideas that the other moms haven't touched upon. But, do realize that this will largely be a problem for daycare. They should be pretty experienced getting little ones transitioned into their setting. They will figure it out. So, do what you can, but don't worry overly much. Transitions can be rough, but you will all get through it. Also, remember that children are often more pliable for others than for their moms. They know they've got us wrapped around their fingers.
Baby's calling. Good luck!