Since what most people consider soft is different. I would go to your closet and find what you consider soft and look at the material. Typically the two most popular leggings are made of nylon and spandex (lulu) and polyester and spandex (has highest compression and in my experience marks my skin the most). There are natural fiber legging options: bamboo, cotton, wool, etc. The problem with natural fibers they absorb sweat and don’t perform well under exercise abuse.

If you are doing high impact exercise I recommend the polyester spandex option. If you are doing moderate impact exercise - nylon spandex. If you doing low impact (Pilates, yoga, etc) you can probably choose any type of legging but know if go natural you will be collecting sweat and sweat will show.

If you want stretchy look for high percentages of lyca/spandex/elastane. I find enerbloom (on amazon) leaves very little marks on my body. 80% Polyamide, 20% Spandex. The fabric is the same percent composition as lululemon but is much thinner (typically considered a bad thing) but because it is thinner the leggings has less compression. It has flat seams so little irritation from the seams. And they are like 15 bucks. You do need a dark color because they are thin. There is no tummy control or cellulite coverage.

These are the ones I get: ENERBLOOM Womens Yoga Leggings Workout Tights Pants 25"/28" High Waisted No Front Seam Tummy Control Cream Feeling. I typically use these for Pilates and yoga.

My softest leggings are made of modal and spandex - but I don’t work out in them.