L.M.
I was walking for about 45 minutes to an hour for the first couple of months. I did the Billy Blanks Tae-Bo 'Flex' workout every day starting at about 4 months in, all the way through to the end, and it was great. I think I began skipping the jumping jacks towards the later part of the 8th month, but everything else was low impact enough to work well the whole time. It's a fairly old video by now, so you'll probably be able to get it online pretty cheap. Best wishes!
-L.