I was in exactly the same position, and managed to lose 3 stone in just a few months by calorie counting, courtesy of myfitnesspal. You don't want to reduce your intake by too much while you're still breastfeeding though so I wouldn't suggest dropping to 500 calories a day (a la 5:2) as that might affect your supply.
Cooking from scratch, even simple meals, is a good way of controlling what you eat, so have a think about what you can manage to make quickly. And if you can fit in any exercise that will make a big difference, not just to weight loss, toning but general sense of well being (it did for me anyway).
Best of luck - and try to join one of the many support threads on here when you get started, a bit of accountability (even if it's online and anonymous) makes all the difference
MFP is indeed a wonderful website : it really lets you find out what you are eating and thus helps to adjust it
5:2 and breastfeeding seems to be working fine for the ladies on the threads that do it - no worries on milk supply because your milk is not directly related to preceding meals unless you are incredibly thin
and YYYY yo exercise and toning - toned muscle takes up less space than flabbier muscle so you shrink while still enjoying healthy food
Thanks for your responses. I really miss exercise but when I tried to take up running again recently I found the stress of trying to fit it into my days a nightmare! Hmm I guess I'll just have to find a way
normal balance of food; 40% good carbs (potatoes, rice, bread, pasta and veg), loads more veg (as much as you like), some dairy, a little fat, some protein. As little as possible of the sugary stuff. No diet food, no low-fat food (full of sugar), no ready meals (solid junk) etc etc. No shakes, no supplements, no similar nonsense.
normal intake is about 2000 calories a day, so go to about 1800 and move around a bit and you'll lose weight, especially as it transfers to the baby. 3 stone will take about 18 months, maybe a bit less. Any faster and it will go straight on again with interest. Diets and fad diets especially don't work, that's why there's so much money in it.
in a tin or frozen doesn't always mean bad. Serve less to yourself than your husband. If your toddler doesn't eat much, serve less - she/he can always ask for more, reduces waste and stops you cleaning her plate!
when you do feel like cooking, make double or more and freeze.