You need backpaks or tact vests to improve both of them. Some armor helps you bear more mass and bulk but they are pretty middle / late game.

Also the body type of you paws influence those (as in you'll have hard times to fit a grenade launcher, an anti materiel rifle and 30 kg of armors on a slim pawn with wooden arms). Same things for health stats (some of them can have a huge impact, like manipulation I think); At last, you can edit a value in a mod to improve the base stat for mass and bulk, but i do not remember the name of it.

Edit :
https://steamcommunity.com/workshop/filedetails/discussion/1631756268/5691968038972465758/

I put mine to 50 mass and 30 bulk instead of 40/20, it's better I find and not enough to break the balance.