This is a tough one! I struggle with this too, especially since I hit menopause. Before, I could lose weight mainly by watching what I eat, now it's not so simple.
I've found that there are some exercises I can do, like stationary cycling and water exercise. I can lift light, 1 or 2 lb. weights. There are videos out there for arthritics that let you do simple yoga moves, often while sitting in a chair.
Track what you eat, every mouthful. You can do this on paper, or use a free online program like MyFitnessPal. This sit also lets you track calories burned in activities and exercise. I found through tracking that I am prone to a lot of mindless snacking. I work from home so the kitchen is ALWAYS open! :)
Drink lots and lots of water, a MINIMUM of 8 cups a day. I have a refillable water bottle that holds 8 cups and I try to drink it up at least once a day. Flavoring it with lemon juice or crystal light packets helps it go down.
Hope this helps!
Thank you for your comment. I will surely use your advice.