hi there,
I'm in the same boat with my son. I got this thing from wal-mart (not sure what it's called) that's just a piece of fabric held together by wire, and one end of it is raised, so you just lay the baby on it (with their head on the raised end obviously) in the big bath tub. It was only about $5 so a really good investment, and bath time is a lot easier than trying to squeeze him into that tiny infant tub!
Whiskers