Aerobic cross-training refers to using two to three different types of aerobic exercise during an exercise session, you may start your plan with 60 minutes:
20 minutes of walking or jogging;
20 minutes of biking;
20 minutes of rowing.
Something simple like a ten minute walk followed by ten minutes with an exercise video. Gradually build up from there. You can use in your cross-training program: walking, jogging, biking, rowing, stair climbing, swimming, exercise videos, etc. Any combination of aerobic exercises will do. You simply go from one to the next with very little time between them.