I have an idea to inprove inventory with backpacks. I know im not the first one who say that but. My idea to have 3 levels backpack system. First thing first in inventory would be add back slot where you can place one unstackable tool or backpack. Backpack shoud't have ro be cheap. And each level cost more chest and leather. All backpacks are made not from iron or diamond.
Small backpack add 9 inventory slots.(total 45).
Medium backpack add 18 inventory slots. (Total 54).
And then you can upgrade to even more space or crafting table.
Big backpack add 27 inventory slots. (Total 63)
Or crafting backpack add 18 slots and with it you can access 3 by 3 crafting grid in inventory.
I personaly think backpacks shoud be added but they shoud replace egsisting inventory and a little big expande it.