One-bag with item type auto-sort. I've modded it to use sensible categorization/auto sorting for both leveling and end-game Vanilla 1.12.
https://github.com/Brqje/EngInventory
Modifications in a nutshell:
Updated TOC for 1.12
Extended bag slot support from 109 slots to 128 slots (16-slot main bag & 4x 28-slot bag)
Modified OpenAllBags hook to allow Blizzard "Open All Bags" keybind to actually toggle, instead of just open bags (similar to default UI behaviour)
Modified default settings: scale from 0.64 to 1 and columns from 9 to 10
Modified categorization groups
Modified categorization string search patterns
Added over 300 items to specifically categorize (default override)
Scroll down on GitHub page for a full explanation.
Difference examples, EngInventory original version vs edited version:
Rogue
Original version left / Baroque edit right
Mage
Original version left / Baroque edit right
Warrior
Original version left / Baroque edit right
Screenshot taken while testing consumable categorization: