A Whenever you're considering a change in parenting styles, it helps to put yourself in your child's place to see things from his point of view. That way, you're able to make decisions that take the needs of all family members into account. Your child has been sleeping in what he considers ideal circumstances for 18 months, nestled safely next to his favorite people - naturally he loves this "night life"! So any smart child is unlikely to accept a downgrade without a fuss. The good news is that the sensitivity you've developed by sleeping side by side for so long can help you send your son the message - verbally and non-verbally - that it's okay for him to move to his own bed. If he senses that you have any ambivalence or anxiety about moving him out, he's likely to cling to the family bed a bit longer.
If you're still breastfeeding, don't expect your toddler to wean from your bed and your breast all at once. One way that may ease the transition is to put a toddler mattress at the foot of your bed and lie down next to him at night and nurse a while, letting him get used to a different space for sleeping. Having Dad take over nighttime parenting duty may be a big help, too. Dad can rock your toddler to sleep, or lie next to him on the mattress on the floor. (If your son falls into a deep sleep while rocking, Dad can then ease him into the toddler bed.) When your son wakes up, protesting loudly about his new solo sleeping arrangement, your spouse can then become the main comforter at night. (Your child is more likely to accept help going back to sleep from the same person who put him to sleep.) Another tip: Play a continuous-tape recording of your son's favorite lullabies, or, even better, make a medley of you speaking and singing to him. If your toddler goes to bed hearing the tape, he's more likely to go back to sleep when he hears it upon awakening.
Increasing the time during the day you spend fostering your attachment to your son can also help ease him into sleeping on his own at night. Spend a lot of time holding him and playing with him; you might even take a nap nestled together. Healthy weaning from any form of attachment should follow one general principle: It's best to let Baby wean from his parents rather than the other way around. Which is not to say that your son won't need a little encouragement from you. If you aren't making headway on your experiment with solo sleeping, put the project on hold for a couple of months, then try again.