All my kids moved out and I've taken over the boys bedroom with fabric (quilting and garment sewing)
We live in a 1915 Craftsman, and the room has carpeting that will not be removed, so the floors are uneven.
I bought some metal shelves from Home Depot, there are 4 shelves, each 2' x 3 ', 5 units.
My husband attached each shelving unit to the wall with zip ties that hook to an eye bolt screwed into the studs of the wall. No matter how uneven I make them, those shelves are not falling!

I store my threads in an Alex drawer unit from Ikea. The unit is on casters and rolls under my sewing table but can also be rolled beside the table to help support large projects. Some drawers have some spice jar holders in them (also from Ikea) that hold threads that need to be horizontal so that I can see the colours. thread cones do not fit in any of these drawers though.

Clear long narrow plastic boxes...under my bed, under my couch, on the foot pump of my antique treadle, in drawers that should have clothes in them, far corners bottom (and top) of my closet. Recently worked on quilts are filed into shoe boxes in my bedroom corner and even closer to being done ones are kept in large old baskets so they're handy. Just almost ready to decide which pattern are placed in clear stacking plastic cases Threads and such have their own boxes so I can find them easier.