I've got a couple of sticking points with the inventory overall, and some QoL possibilities to fix them:

• What's the point in having a grid-based inventory system if everything is the same size? I get that you're in a tough spot here where anything you do will look like you're copying the game the genre is named for, but there's no good reason a glove and a 2-handed axe should take up the same amount of inventory space. Many items should be larger. And this brings me to my next point..
• Even with the way the inventory is at present (with items being "smaller" than they should be), there's just not enough space. I shouldn't run out of space halfway through a floor of a dungeon when I'm only picking up rare items. The inventory should be somewhere between 1.5x to 2x its current size. I wouldn't mind leaving it how it is and having the ability to unlock more inventory space either through story or endgame progression. But if you make items larger as I suggested above, you would at least need to expand to 1.5x to keep up with that.
• I've seen others mention this, but in lieu of or in addition to a larger inventory, a way to sell during missions without going back to town is crucial. There really isn't a good reason to limit the already limited gold. The trade shrines at the end of expedition floors are a great addition - why not have them scattered out a bit more in the world?
• I don't really dislike this one, but your design choice to have two different shoulderplates and two different gloves is just weird to me. You could have used those slots for something more interesting, like a cape or a trinket or something. This isn't so much QoL as just a suggestion in general.

Thanks for reading.