Denise Austin's aerobics DVDs have low impact options. I have one called "Denise Austin's Personal Training System" that lets you choose a customized workout by choosing cardio, upper body, lower body, ab &/or stretching segments. You can also choose low or high impact cardio. The moves are pretty basic.
If you do a search for "Denise Austin aerobic" on YouTube, there are several workouts to try to see if you like her style. : )