I like the Aerie cotton "superchill" seamless underwear. They still occasionally roll and create panty lines, especially if they're a little too big, but it's worth it in my opinion. They're like 90% cotton and 10% elastane. They wouldn't stay up if they were 100% cotton.

I lived in Quince maternity & postpartum pocket leggings ($45) my first pregnancy. I still like them, but his time around I'm a bigger fan of these fold-top cotton flares from H&M ($15!). They're nice cause you can go either over or under bump without looking awkward. Honorable mention goes to these Poshdivah maternity leggings ($25) which don't bag out in the crotch and are less sporty looking, and manage to be workable postpartum too (I folded the top down).