my advise would be to set your steps to say 500 every hour and this will make you get up every hour and move, even if those steps are up and down the stairs or living room to kitchen and back. 500 steps every hour 12 hrs a day is 6000 steps a day. walk for you paper or to the local shop rather than drive. get off the bus one stop before your normal one i
also adds a bit with little effort.
Good luck remeber fitness is not only about what you weight, maybe eating one less potato/sandwich/ biscuit and look at what you eat and even eating the same amount of something healthier. Porridge is the best start to the day, I eat mine cold and uncooked having soaked it overnight
I've got another 'keen'... Ouch!