I have found myself with the same dilemma. Although my man bits are not overly large, the proper fit is still an issue.
So, I have a sewing machine. Ill buy panties in size large and also in a smaller size. What I do is take the back half of smaller pair and add it to the front of larger one. I will use fabric glue or stitching depends on the fabric type. This allows the panties to sit higher since I dont have hips to hold them up and also plenty of room in the front.