New Legs for Karlstad sofa by Uncle Bob's Workshop
Custom designed, mid century modern styled legs are a better fit for this than the stock ones from IKEA. These legs screw right into the existing holes in the frame, so no modifications or tools are needed.
You can find them here, www.unclebobsworkshop.com/
Direct link to the product: www.unclebobsworkshop.com/product/furniture-legs/
EDIT: it appears that Uncle Bob is doing business through his primary website only. His etsy page seems to have been taken down.