I did Weight Watchers for 6 months before beginning TTC and lost just over 25 lbs. If you consider that a pound a week or 5 pounds a month is considered healthy loss, you could probably lose 30. I am a carb lover and was not willing to go low carb, but I loved that Weight Watchers controlled my portions without dictating my carbs and/or foods. I dropped my A1c by nearly a point and dropped my pump TDD (total daily dosage) to 30 units from over 40 units, which I felt was drastic (and great). I was bolusing less because I was eating healthily.
I have a lot of tips I could give you, but my biggest tip comes from my CDE. You have to start acting, eating, and monitoring as though you are already pregnant. Then, the only variable you add to your routine is the baby. That helped keep me focused and mindful. And since I hadn't been green-lighted for TTC yet, it gave me six months of feeling like I was in control and doing something proactive for my health.