Hi Five times nice question.
It's funny you should ask as Im on a regime at the moment after dislocating my knee Im not able to do much running but can swim, cycle and go on the cross trainer. Im also following a pretty strict diet which has been so successful Im considering sending it off to More Magazine for its readers to enjoy.
1)- Diet. I call this the Philadelphia and Weight Watchers bread diet. You have once piece of the bread with a thick layer of Philadelphia on it for breakfast. Lunchtime you can have the same but two pieces of bread and maybe a digestive or two. Dinner time you can eat what you want but try to be balanced i.e a donner kebab will undo the days hard work. Its also important to cut down on snacks and look at other alternatives to crisps/chocolate. I personally find the go ahead range of salt and vinegar mini rice cakes are an excellent low fat alternative to space invader crisps.
2) Exercise. This is where I come into my own, Im a supreme athlete and can turn my hand to pretty much any sport with ease Im not sure what your capabilities are in this area but its important to find what you enjoy/are better at. Join a gym if you want to and have a go at swimming, rowing, running, cycling, cross trainer and find which you enjoy the most. If you are not a gym person you can simply do repetitions of press ups/pull ups/sit ups which if you follow in conjunction with my diet you're body will change for the better.
3) Mental. I'm glad you mentioned this. People often forget how important mental strength is when following a regime. It's the thing that stops you eating that steak and ale pie, or makes you go to the gym on a Friday night if you master this, you're half way to being like me. To help you, this is a little mantra that Im finding useful at the moment.
'nothing tastes as good as thin feels'
Again- kudos on your question I hope you enjoyed reading it as much as I enjoyed writing it.
Your mate
HRH.