My daughter is nine months old, too, and I worry about the same thing. It seems like she's been on the verge of crawling for months now, but she doesn't crawl. She gets around, though, so I try not to worry. (She squirms and rolls.)
I worry, too, because she doesn't pull up on things (my three previous children, different father, were all preparing to walk at this point) and doesn't say anything intentionally. (She says "dada" a lot, but I don't know if she's talking about her dad.) She makes lots of noises but no real words. It's hard not to worry about our children, isn't it?
I wonder if your son would like something that helps him move, like the Jumperoo we were given? With a little kicking action from my daughter she gets a little extra bounce, which she loves.