Minimal user interface intrusion, in fact none. I used the existing numerical value as the trigger. 

All Vanilla operations still work as usual.
The bottom right corner of all inventory items is the HOTSPOT for my mod. 

1. Hover over bottom right corner of an item.
2. Scroll mouse wheel to set a quanity.
3. Right click that number to drop / transfer that amount.
4. Left Click Drag and Drop that number to manually place where desired.

Limitation I hope to address later.

Due to how the system handles the players gear, there are some limitations, for example when retreiving from the ground by RMB on number, the transfer goes to the vest over backback and is limited in transfer amount by the compartment setup of the vest. So 12 items on ground will transfer as 4 x 4 x 4. Still reduces 12 clicks to 3, so there is that ;)  Other limitations exists but in short, as or right now, LMB number drag to a backback is full transfer unless backpack reaches capacity, in which case only the amount that will fit will be transfered.

Find me on Discord to report any bugs. This is very much a Work In Progress.

Inventory Stack Quick Move

1.0.73

1.0.72

1.0.71

1.0.70

1.0.69