Yep, I too am the heaviest ever - I've put on 15 kilos since our wedding in march 07. I am 166cm and weighed in at 93kg last week - i was horrified! I had gone dress shopping the weekend before for a bridesmaid dress for a wedding we are in in Jan and was at least 2 sizes bigger, so that was the kcik up the butt I needed.
That week, I joined Weightwatchers online and so far, so good. I've been doing it for 2 weeks now. They have a special allowance for breastfeeding mums - so if you do the points plan, you get an extra 7 points (or it could be 9, can't remember!) and some days, I struggle to eat all the points - which they stress you must do if you are breastfeeding. Because its online, I log in in the morning and plan my meals for the day - they have heaps of foods stored on there so you don't have to work anything out yourself, they also have recipes as well, and then as the day progresses, I add in any snacks. You can earn bonus points if you exercise as well. I'm finding it pretty easy to stick to, and seem to eat plenty. I've done it before and i find its a great way as it makes you think about portion sizes and healthy choices.