Something to consider when crafting is that, as your crafting skill gets higher, you reach a point where you can produce HQ items from NQ mats. When you reach this point, you can start converting HQ mats to NQ, which reduces the number of stacks. I suppose you could sell the HQ mats, but to each their own.

Avoiding collecting stacks of "intermediary" mats. For example, don't have stacks of lumber; just craft logs into lumber when needed. Likewise collect ores for crafting into ingots. In either case, since you can craft HQ items from NQ mats, you can use Quick Synthesis to produce the intermediary mats, as needed.

In addition to the crafting guild vendors, the beast tribe vendors have mats that you can obtain when needed, as opposed to storing stacks of the stuff. I wouldn't seriously use this method, but just throwing it out there.

All that said, I've commented in the past that there's a form a "storage space deflation" that occurs when, over the course of years, more stuff is added to the game, but your inventory space remains fixed. However, someone pointed out that wonky code underlies the inventory system, such that increasing the available slots is prohibitive.