This mod makes backpacks increase your inventory grid size, not just carry weight.

Features:

• Detects which backpack is equipped.
• Applies different bonus inventory rows per backpack type.
• Dynamically resizes the inventory when you equip or unequip a backpack.
• Safely prevents item loss by canceling size reduction if there is not enough space. (If you wish that the items drop to the ground let me know)
• In short: bigger backpacks now feel like bigger backpacks, with visible extra storage space in your inventory UI.

DISCLAMER:
It looks a bit wanky when the inventory gets expanded because it was not build for that. And i dont know how it will look on diffrent monitors.