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 curtains, light blocking, 1 pair (203.410.36) - reviews, price, where to buy
New Other - Ikea MAJGULL Blackout curtains, 1 pair, dark turquoise 57x98 " | eBay
MAJGULL dimming curtains, 1 pair (504.177.89) - reviews, price, where to buy