It's hard doing any exercise at the moment, really, because I am so big
Any moving around is exercise so do what you can. You tell any person who is a healthy weight to carry 4 stone around all day and they'll find that next to impossible. So do what you can and your own body with provide resistance and weight training. Losing your weight just changes the types of exercise you can do and you can up the intensity 
Ok, so firstly a bit about me so you have context. I'm a diagnosed binge eater. I've successfully dropped all my weight 3 times and regained, but not to the extent I was. First time was 6.5 stone, second 6 stone, third 4 stone. My doctor recommended Lighterlife 12 years ago. It's similar to Cambridge but with additional input to try to identify the psychology behind our issues. I learnt that I feel safer when I'm big, I was raped as a teenager. I've used Cambridge and Exante to break the cycle by removing all conventional food and then moved onto higher plans which include conventional food and moved up through the plans to help me find the balance. It all goes wrong for me when I feel exposed to risk and quickly seek my fat blanket to feel safe again. My required blanket is getting thinner each time.
You'll get a lot of advice about what you SHOULD be doing. I hate that word, 'should'. 😡
This is all about finding out how/why/what/when/when you eat is more important than being healthy? I believe that most of us who are largely overweight KNOW what we should and shouldn't be doing and the effects of our destructive habits, yet our temporary diet/lifestyle doesn't become a sustainable long term change and we regain. The question is why? It's not just about what we eat, but why?
My biggest tip is to do a food/thought diary.
In this you don't just record what you eat, you record any time you want to but don't. You need to think about context. So record the time, the place, what you were doing and your emotions, what you fancied eating.
Chances are you'll find a pattern. These are your triggers and flash points. From there you can work out how you can best challenge those triggers and break the cycle of how you react to them.
My trigger feelings were guilt at having a good life (I wanted to punish myself for not reporting my rapist who I know continued with subsequent partners) and feeling powerless when I felt I wasn't being listened to or my opinion considered.
My trigger times were just before DD got home from school and after she went to bed. My foods were cheese and cake. I could eat 3 days of calories in one sitting and not realized id done it until I physically couldn't stuff anymore in. When it happened it was like being in a trance, doing it bought me nothingness, so peace.
A complete meal replacement plan is the only way I've ever got anywhere with my weight and believe me, I've tried everything! Breaking the cycle of reliance on conventional food is the key for me.
I can't recommend a diet for you as we are all different, as is our solutions, the only thing I'd say is right for everyone is to write your diary focussing on the circumstances, rather than calorie counting as it's about understanding yourself and working out what you need to change.
Best of luck. 