Thanks for the tips. I did a search on Amazon for all the seats that have LATCH and found the Britax, which is the brand we have been using and liking the most so far. I like the Secure Guard on that, too. I'm not planning to move him til he's at least 40 lbs, but he's getting very close, and the way he's eating, he could well be there next week! ;-) So I'm doing my research now in preparation for the day that I look back and his shoulders are too far above the straps in his current seat.
Oh, and even though as of now I'd prefer it, LATCH is not as important as a good seat that fits him well, so if anyone feels there is a better seat for a smaller/narrower kid, feel free to share! He doesn't ride in the car every day, so remembering to buckle the seat down might be a problem, but it's worth a try for a better (and less expensive) seat.