Hey! Congratulations on the loss already that is Amazeballs!!!!
I agree with a lot of what was said above, swimming is low impact and easier on the joints so it's a good one, there are even some places that offer areobics in the water for heavier people that are really good. The water both helps lift the weight off your joints AND adds resistance so that's double awesome.
Chair exercises is a great way to go too!
If you are able to walk 10 mins comfortably, then keep that up... but if 10 is your MAX before the pain/exhaustion sets in, I would suggest cutting it down to 5 and couple it with something else like chair exercises (Thank you Youtube). It's not good to push yourself to the MAX every time, let your body get there in it's own time.. pushing yourself too hard can result in injuries and setbacks in your progress.
You got this!!!