One solution to elastic around the underwear....I discovered elastic is what was really irritating my skin. What I did was to turn the elastic to the pretty side of my underwear so NO elastic was touching my skin.
I then machine sewed the elastic in place while stretching out the undies so the stitches wouldn't rip. This prevented the elastic from irritating me because it does not touch your skin.
I know it sounds weird and strange but it was a game changer for me.
I also switch to boy undies when I have a flare but I haven't found any that are all cotton which is more soothing to the skin than a man made fiber.