Well, as you already know, to lose 1 lb, you need to burn 3500 calories.
If you want to lose 1 lb per week, eat 500 calories less than you burn each day (there are charts available on the web that can help you estimated how much you burn based on age/height/weight/etc.).
So, e.g., I am a person who burns approximately 2000 calories a day based on my stats. To lose a pound per week, I must eat only 1500 a day.
However, if I add exercise into the mix - say, for example, I walk briskly for 30 minutes, which burns 178 calories - then I can either:
Eat an additional 178 calories on top of my already allotted 1500 to continue my goal of losing 1lb per week
OR
Don't eat anything additional, stick to my 1500, and I will wind up losing a little more than 1 lb per week
The more calories you burn, the more fat you burn.
Also, exercise adds tone to your figure and can help suppress the appetite.
From the sounds of it, walking is your best bet at the moment - just work your way slowly up to a more brisk pace - e.g. 4 mph.
Also, maybe a recumbent bike?
Best of luck!