I lost a significant amount of weight about six years ago and have maintained an ideal BMI/body habitus since then.

While you certainly need discipline and a plan, it definitely does not need to affect your FF/premium cabin habits. Unless you're flying in F every day or two and consuming ridiculous amounts of calories, you can still enjoy the typical F meal, even drinks, and still lose weight. Make sure you're keeping track of your eating habits somehow (Excel spreadsheet calorie counter or something similar).

You can always compensate on other days. It's a marathon, not a sprint.