The first requirement is that you must know your body size. Have a professional tailor measure or do it yourself. Your job is half done in finding the right Kurti, once you have the magic numbers.
Get your favourite fabric sewn to this size or as every online store will provide a size chart for the dress, find your size and choose the best fit. But keep in mind that there is no universal size chart for Kurtis. This can vary between stores or even with the brand of the fabric. So make sure to choose the right one every time you search.