When we had the sauce done, I pulled out the dough to see whether it had risen enough. Nope - in fact it hadn't risen at all. It seemed we shouldn't have taken the risk with that old yeast after all. In a last-ditch attempt to make it rise, I sat the bowl on top of the oven where it would be really nice and warm.
Ok, so here's something a little embarrassing...
I came home today (having already written the above) and Joska says to me "so I read that recipe, and you're supposed to puree the sauce". I checked, and sure enough, there it is on the last line: "puree tomato mixture". Oops. So I guess the sauce wasn't supposed to be chunky after all. But never mind, it still tasted pretty great.