GML Isometric RPGs: Tiles and Sprite Origins

[FacesOfMu]

I'm not sure if this should be posted in Programming or Game Design threads. I'm wondering what the norm is when it comes to deciding the origins of sprites for an isometric RPG? I've got sprites that will be drawn in both inventory and in the room grid.
When they're in the room grid, I need the origins to be at the "base" so the player can walk in front and behind them properly. I also want objects I place in the room to snap to grid.
But when they're in inventory, I need the origin to be in the top left corner of the inventory grid slot.

What's the most adopted approach when it comes to setting origins and drawing them in games like this?

 

[FacesOfMu]

I think....I could have everything if I could choose snap-to-grid to not use origins but to snap to a side or corner of the sprite that I choose. So if I could set snap-to-grid for the room to be "bottom left corner of sprite", then I could put the origin to the center of the base (or anywhere needed), put instances in line with my room grid, do a little maths for my inventory slots, and my player and other instances would walk around the object in the room correctly.