Re: Sewing Karlstad covers (to repair separating seam)
sorry to be seeing this so late. In the event that it's still helpful, I would suggest discussing the problem with an upholsterer. I assume you're talking about an upholstered piece vs. a slipcover, right? It's possible but unlikely it could be sewn by hand from the public side somehow. More likely the piece would need to be divested of it's upholstery cover, sewn, and reinstalled. If it's just a slipcover your problem is much simpler. Take off the cover and reinforce the problem areas (a tailor shop could probably do it).
If IKEA were a drug I'd be labeled a heavy user.