HACK - I attached my MAJGULL blackout curtains to my SANELA curtains using leftover RIKTIG wire curtain hooks. Way easier than everything that I was thinking of doing. It looks and works
MAJGULL light grey, Room darkening curtains, 1 pair, 145x250 cm - IKEA | Curtains with blinds, Block out curtains, Curtain decor
MAJGULL curtains, light blocking, 1 pair (203.410.36) - reviews, price, where to buy