Welcome, countess!
I think a stone by Christmas would be absolutely doable. The best advice I can give you would be to buy/read a couple of good books on low carbing. The three I have/like are:
Dr Atkins - The New Diet Revolution
This is really the low carb bible, and it goes into a lot of detail about the science behind the whole thing. It works on the basis of three phases, the first of which (induction) is the most strict. This is for two weeks, and you have to limit your carbs to 20g per day, consuming them in the form of salad/veg along with unprocessed meat/fish. Don't be fooled by anything you have read or seen in the media. The emphasis is on fresh, natural (i.e. unprocessed foods), and while meat/fish tend to be the centre of a meal, you are very much encouraged to eat salad and veg to get your carbs. You are also able to eat foods that you will have long since considered 'forbidden' - cheese, cream, butter, olive oil - and it will seem very, very counter-intuitive to be eating these foods. It felt like a huge leap of faith for me to sit down to plates of food that previously (following a low fat/low calorie diet) would have been forbidden!
But it's not unheard of for people to lose a good 10lbs or so in this phase of the diet.
Charles Clarke, The High Protein Diet
Less strict and, if I remember rightly, doesn't have any phases, just 'dive straight in', this is based on 60g of carbs a day. You can have one slice of wholemeal bread a day, which makes breakfasts more flexible and also an orange a day.
India Knight/Neris Thomas - The Idiot Proof Diet
A very good book that was written by two women who created and, most importantly, followed the diet. They both, apparently, lost 5 stone. It's easy to read and takes into account the psychological side of dieting as well. There's much less science in here, and it's a bit less strict, but it still works around 3 phases and aims to get you, by phase 3, eating some carbs again. There's also a very good recipe book to go with the main book, with some lovely, lovely recipes that all the family will enjoy, which is key - means you and the family are all eating the same thing. Don't just buy the recipe book though, as it doesn't give any of their thinking behind their approach.
There is another book which I have recently read which I am very interested in, although I haven't yet started to put it into practice, which is:
Zoe Harcombe, The Harcombe Diet
Although essentially a low carb plan, this is based around the theory that weight gain/difficulting losing weight can be exacerbated by the presence of three medical conditions: candida, food intolerance and/or hypoglycaemia. Again there are three phases, the first of which is the most strict and which lasts for 5 days. This is an anti-candida phase, and it can be quite hard to follow, but if you suffer from any of these conditions (and often people suffer from at least two - and not always without realising), then avoiding/cutting out carbs can make a huge difference.
Of course, you don't really need a book, or to follow a specific plan - I have never done Atkins properly - but it does really help to know what you can eat and what you can't, as well as why.
Or, you could also follow my Cunning Plan (I think I shall have to copyright/trade mark this 
).....