Storing large format art in the smallest space possible
If the old portfolio bag worked well, I'd suggest getting another one. It seems to be the most practical solution since it's mobile.
An alternative would be having a drawing cabinet and installing it atop an existing closet or a tall wooden construction so the space underneath is still available.
There are also vertical drawing cabinets (e.g. image 2) available, that won't take up as much floor space, and might be easier to hang from a wall.










Image 1 (source)
Image 2 (source)




These are usually quite expensive, though, but you can often find them as second hand offerings on online market place websites.
Alternatively, you can use them as references to build your own - that way, you can adapt them completely to your desired volume, shape, and location.