I found this amazing model on printables and designed an adapter so you could put it over the RÅSEGEL table light. Very decorative! I used PLA, and you realy need brim, otherwise the print will probably fail (tested for you). If you dont like the brim on the lampshade itself, you can either trim or cut it all off. Personally I just cut the floral edges and ended up with a circular top.

https://www.ikea.com/de/de/p/rasegel-tischleuchte-00462656/