If you are stil BFg, i wont suggest excessive exercise as your body will produce something which may affect the taste of BM ( i read it some where), if you need to, please express b4 you go.
Yoga is a good form of exercise, i wanted to do while on maternity leave BUT the yoga instructor that i know told me only can do it after 6-9mth, ONLY can do simple breathing exercise during that few months.
Aerobic, i would suggest you let the instructor know that you are how many mth after delivery, some movement like jumping/hopping may not be good for you, especially so if you delivered via cesearean, which is in my case.
Always the instructor know about your condition before you go into form of exercise.
Happy working out.