Non weight barring cardio and strength training

I have lost a total of 75 pounds and got 75 more to go. After working out hard last month I started having problems with my right knee. After xray, mri, I was told I have a hole in my cartilage under my knee cap. I will be have a cartilage transfer next month and told I'll be non weight barring for 8-12 weeks.
I need some good workout ideas I can do while sitting without doing anymore damage to it now and after surgery.
Strength training is good and i got ideas for that but I was doing interval treadmill training daily for cardio plus I walked on average 5-7 miles daily at work.
I don't want to gain, hopefully maintain but the goal is to still lose weight during this process.