T.,
Wow! You sound like me! I exclusively nursed my daughter Grace (now 3 yrs)-- and often she'd fall asleep after nursing and I'd put her down. I, like you, worried about this all the time. And I always thought there was a "right" way to do it-- but that I just didn't know what that right way was. I was convinced that someone out there knew a secret that I didn't know! Guess what? There is no secret.
Your son is sleeping through the night. That's great! He's sleeping, so you're sleeping-- and a rested mom is half the battle.
I'll tell you where we are at now that Grace is 37 months. When she was one she settled into a two nap a day pattern (both, nursed and rocked down to sleep). When she was two she (not me) dropped to one nap (and the start time for that nap has shifted since then from 12:30 to 2:00 p.m.). The most important change she made is when we weaned her. Around 12 months we introduced cows milk in Gerber sippy cups. Around 21 months we were only nursing twice a day (for nap and bed)-- and as part of the weaning process, I knew we had to drop one of those. So I started asking my husband to do bedtime. He'd take up a little sippy cup of milk, read stories, say prayers, sing hymns and rock her until she fell asleep. One night, she just asked to be put into bed awake after the "routine"-- and she fell asleep (Eureka!). That's been our routine ever since-- she puts herself to sleep at bed. So now we're down to only one nap-- and, unfortunately, she still needs to be rocked down, but I don't care! Eventually, as she grows into her preschool years, she will no longer require a nap. She's got the important part down-- bedtime.
Believe me, I worried through all those stages. And I'm here today (a survivor-- because Grace did not sleep through the night until 9 mo. and with crying it out-- which was so hard for me, my husband sent me to the basement bedroom with earplugs because my mommy instincts/hormones couldn't take it) to say, your son will learn to sleep on his own. Since he's sleeping all the way through, I wouldn't mess with that pattern for now-- and see how he does later. What's most important is that he gets lots of sleep for good development.
I'm no expert-- and yes, we did read Healthy Sleep Habits Happy Child (which only made me wish I could conjure up a sleep expert to come to my house). Don't worry! You're son is a remarkable sleeper!