Hello there -
I did CIO at 5.5 months for my now 18 month old because she was only sleeping for two hour blocks all night long and I was just absolutely desperate for more sleep. I didn't expect her to sleep all night at that age - I just needed her to go at least three hours between feedings. So I stopped going to her if it had been less than three hours since her last nursing session. It took a little while but it worked and stretched out her feeding schedule enough that I could function.
For naps, what I do is leave her alone for (at least) 60 minutes, no matter what. If she was still awake after this time, I'd go to her. This has meant that she's had a few non-naps where she cried for the whole hour, but mostly she has slept. Now she almost always naps for 2-3 hours. She's also quite happy to hang out and relax in her crib. On the exceptionally rare days that she doesn't get enough nap, then I just adjust her schedule slightly so her next sleep period comes a little bit earlier (and I try to be flexible with her as we get close to that time, because I know she's likely to be a little cranky because she's tired.)
As far as the comment that CIO causes children to be insecure - everyone who meets her will tell you that my daughter is one of the most outgoing, happy, sunshiney little girls you will ever meet. She tells me about a thousand times a day that she is happy, and she is independent and absolutely _not_ clingy. So don't worry that it'll hurt your son!
Good luck to you! He'll figure out a good sleep schedule soon with you being consistent.
HP