Hi Lynn,
Wow, your recovery sounds very good at 6 weeks post surgery. I am 2.5 years post and I remember what I felt like at 6 weeks. I did get into cardio rehab at about 8 weeks and it worked wonders for me.
Please consider doing this if you can!. I signed up for an 8 AM class and it lasts about 1 hour. I went to work after the class. My hospital also had a 7 AM class but that was too early for me !!! They put a wireless EKG on each of us and monitored us throughout the hour. If they saw any anomolies (a-fib, too high a rate), they would run over and slow us down. They reallly helped to speed my recovery. I realized during that class how much I used (pre-op) to over do it during exercise. By this, I mean pushing myself too hard.
Also, don't be in too big a hurry to back to full time work. This surgery is very hard on your body, and rest and mild exercise like walking is great. You really need to get the rest you need to get back to full power. Working too hard too early could cause a set back in your recovery. "Pain is not the sign of weakness leaving the body !"
As for the weights and exercises I would recommend asking your cardio. He knows you condition better than anyone.
Good luck,
Jim