First, congratulations for recognizing that you need to lose weight. You've taken the first step.
Second, don't plan to "hit back to gym soon and work hard on the cardio." That doesn't usually work. If you can go for a walk right now, go for a 30 mins walk. If not, perform 10 squats. If possible, do jumping jacks (modify it if you cannot lift yourself) for 15 seconds. That's not planning; that's doing. Countless people plan to lose weight without actually doing something. Don't waste time planning; jump in and start doing something.
Third, diet is an integral part and I'm glad you realize that. Starting tomorrow (or today, depending on the time) start your day with a protein-filled and fiber-filled breakfast. Make them low calories as best as possible; incorporate vegetables, lean meat, fruits, and nuts in your daily intake (both as food and snack).
Fourth, the most effective metabolism-increasing supplements contain green tea. So, rather than seeking a particular brand, seek supplements that contain green tea. They naturally increase your metabolism and provide you with the energy to be more active.
Fifth, take supplements that are rich in Vitamins B-complex. The vitamins naturally increase your energy level and allow you to be more active. You can also just go to a pharmacy and ask them to give you supplements that increase your energy level; they should provide you with supplements that have Vitamins B along with other nutrients.
In summary, to lose weight: eat right, exercise often (and be active), and take the right supplements (not a requirement, but supplements provide many nutrients that aren't accessible through food alone).
Welcome on your new journey to sculpt your body. Stay in touch for motivation, encouragement, and information on how others are faring on this wonderful journey.