Low Impact + Easy On the Knees Lower Body Workout Recommendations?

Hey Blender Peeps!

I was wondering if you all could help me out and maybe recommend some low impact and easy on the knees workouts for the lower body. I finally was able to begin FB Flex today and that first workout I KNOW will leave me sore tomorrow. I want to intertwin my own independent workouts for core and lower body but because of my joints choosing lower body exercises that I can do are pretty difficult. Maybe anyone with similar issues can help? Any help from anyone is greatly appreciated. Or maybe I shouldn't do lower body at all?

Thank you in advance! Have a Blessed day guys!