L.B.
I regret the time I wasted trying to get my first son to nap in the co-sleeper and later in his crib. It didn't work, and it was frustrating.
In my experience it is MUCH better to accept that many babies don't nap well in cribs. With my second son, I put him in the sling or baby carrier (I preferred a wrap, because the weight was distributed evenly on both shoulders) for most of his daytime naps. He slept longer and I was able to get stuff done instead of rocking him forever in the chair, trying to transfer him to the crib when he was deeply asleep only to see him wake up within minutes.
By the way, I am skeptical about the book Healthy Sleep Habits, Happy Child. Not every baby/toddler can be slotted into his magic formula about how often and how long they "should" be napping. Even in the same family, babies will have very different napping patterns.