how do you make thigh highs stay up while wearing leggings/tights underneath?

i live in somewhere super cold but i still want to wear skirts in the fall and winter. the solution i've found is to wear fleece-lined winter tights/leggings.

i've recently started looking at buying thigh high and knee high socks online, but many people say they just fall down naturally due to ~gravity~. i've seen some advice like sock glue and fashion tape, but those only work on skin, and i'm planning on wearing thigh highs on top of my leggings.

i've also seen sock garters recommended, but i don't quite understand how they work. they're supposed to keep the socks up, but won't the garter itself slide down due to gravity too?

what kinds of methods can i use to keep my thigh highs up?