A lot of pants have waist adjusters now, so you can let out or take in that area as needed. I'm currently 5'4" and ~118lbs, but last season and for years I was ~137lbs and the same pants fit me then and now due to velcro adjusters on the sides of the waist. Most notably I'm a fan or Northface pants for how they fit my proportions, but there are plenty of others to choose from. Where are you located? Folks might be able to recommend somewhere near where you live or ski to try stuff on. Ski clothing is like any other piece of clothing where some people gravitate towards certain brands that fit them better while others don't work for them at all yet everyone else might love them.
On the bibs, I just got the Flylow Moxie this season and LOVE them! They have a zipper on one side that you pull down allowing you to sweep them to the opposite side and pull down anything else you're wearing underneath to use the restroom. It's hard to explain without a visual, but I can attest to the fact that it's super easy and intuitive once you do it!
No need to remove any top layers etc. I'm not sure that every bib has this ability though, so make sure you look for it in the descriptions or seek out some crowdsourcing if it's something you're ordering online and you aren't sure. I definitely wouldn't get a pair that didn't have this ability, I have a pair of pants with suspenders that don't have an easy out for the restroom and it's super annoying!! I'll usually just avoid using the bathroom if I can when wearing those because I have to take off whatever layers are on top of the suspenders and it takes forever.