I have not done the Insanity workout myself either, but I know that it is not recommended for woman who have recently had a baby. This is a very intense workout!
I would recommend starting out with some very simple abdominal exercises to get your core back into shape. That is the part of your body that experiences the most trauma during pregnancy and birth. (I should know, I've had five children, all vaginal, at home births.)
I am currently working on P90X, but I am 4 months post birth AND I am greatly modifying the Ab portion of the workout program. I am concentrating on keeping my transverse abdominals tight before doing any kind of abdominal moves. This is especially important if you, like me, have a separation in your abdominus rectus from pregnancy.
Hope this info helps and good luck with your exercise routine whatever you choose to do!