You'll only need to change the right-hand shifter, and any Shimano 9-speed shifter will work. You may be able to pick one (or even a pair, and only use the RH one) of those up for a lot cheaper than you can find a pair of R440's, which are not as common. Of course, if you want your two shifters to match then the R440's would be best. I'm not sure that you'll notice much of a difference in longevity between the 9-speed and 10-speed stuff, but the 9-speed will be a little cheaper to replace each time.