Any tips how to boost metabolism for petites?

The only thing that helps without gaining weight is, unfortunately, to stop being sedentary. It sucks but it's true. There really isn't a way to get a few hundred extra calories without putting in a lot of effort in the form of activity. The smaller you are the more effort you'll need to put in. It will probably be easier to introduce both exercise and non-exercise activity (be less sedentary) because that tends to be more sustainable.

Edit:
If you have been successfully maintaining your current weight, maybe recomp would be a better option for you? Basically, you don't diet down but you work on increasing your muscle mass while losing body fat extremely slowly so that your weight stays almost the same but your body fat percentage changes. Someone more knowledgable may be able to give you a better explanation.