Underwear?

Helloooo communityy!!!!
Looking for some advice on what to wear under my wedding dress. I will be getting cups sewn in as the top is low cut and has some mesh around the leaf lace. So I'm not wearing a bra, but I'm not sure what to do for underwear. I'm thinking a shaper short so my thighs don't rub and I feel smoothed out (it's an A-line dress though so lumps and bumps aren't my concern, I just don't want my thighs rubbing and getting uncomfortable). Anyone know where I can get nude shaper shorts for a decent price? I am a XL/0plus.
Also, do ppl normally wear their wedding night lingerie under their gown? Or do you just change into it later?
Thanks!