In order to lose weight you will have to be in a caloric deficit, this shouldn’t be news to you.
Once you’ve lost the weight you wanted, you can start eating at your daily caloric maintenance level. This is a big difference from going back to eating the way you used to eat that caused you to gain the weight that you just try to lose.
In other words, if you’ve just gone through a dramatic weight loss you have learned two things:
1) You’ve learned how little food you need to eat to lose weight
2) You know how much food you used to eat that caused you to gain weight
BUT you have one more step to go and that is:
Learning how much food you can eat to MAINTAIN your new weight
This last point is the final step for lasting weight loss. Obviously you can’t go back to eating the way you used to, otherwise you’ll just gain weight again.
On the other hand you don’t want to be on your weight loss diet either otherwise you’ll continue to lose weight. What you need to do is increase your calories to your estimated BMR. From there any extra exercise you do might allow you to eat a bit more food.
Pretty simple stuff. If you stick with a good BMR estimate as your maintenance calorie level you should be fine with maintaining your new lower bodyweight.