This is my proposal for a slim side mounted filament spool holder with simple bearings.

There are five 3D printed parts needed:

• 1x main bracket
• 1x spool roll
• 1x bearing spacer
• 1x inner end cap
• 1x outer end cap

Used printing parameters

• PLA
• 0.6mm nozzle
• 0.2mm layer height
• 4 wall and top/bottom layers
• 50% infill

Most other needed parts are fairly standard

• 1x 185mm aluminium tube, 8x1mm length, i.e. 8mm OD, 6mm ID
• 2x bearings type 608 8x22x7mm
• 2x M3x20mm button head screws with washers
• 1x 6mm plastic dowel
• 1x 3,5x35mm self-tapping screw

Additional modifications

• Replace the standard 550mm PTFE filament tube by one with 800m length
• Add a second tube fitting to the outer end of the rubbery tube duct

I'd be glad to receive some feedback or comments for further improvements.

The shown setup is currently undergoing testing on my Bambu Lab P1S.

Update:

• Added STL files for holding 2kg spools with extra 50mm width.
  This is untested so far, please try at your own risk.
  Just print 1x wide roll and 2x wide bearing spacer and use a 235mm aluminium tube.

Why this design?

• I don't like the original Bambu Lab metal holder - 
  so I didn't like the designs re-using it either
• I liked spool holders with bearings from my earlier printers as I found them 
  to be more reliable, especially with slightly tangled filament
• The bearing-based designs I found for download are comparably bulky