I wear a thong most of the time (even in male mode). I have even learned to use the corner of a locker room when changing so I can hide my bare backside. I have found at times that if I’m wearing dress pants with a thong, I usually have to pull the pants out of my cheeks when standing up.
I like feeling a skirt on my bare bum. But most of the time it doesn’t happen. In the colder months, I am wearing (opaque) tights over them. In the in-between months, I am wearing pantyhose over them. Both the tights and pantyhose tend to flatten any bulge. In the warmer months I could wear the skirt directly over the thong. But I’m often going out for a brisk walk. This pushes the skirt front against me, and it feels like it may show a slight bump. So even though I’m wearing a thong, I usually wear a lightweight panty-girdle on top to ensure a flat front even if the skirt is pressed to my legs.