I've tied baby comforters for years. I use a baby weight yarn. I usually tie every 4 to 5 inches. I've never had a problem. I cut the yarn ends about 1 inch. The yarn will fray a little after a few washings. I also use a polyester high pile batting for tie comforters.
Years ago I called one of these blankets a quilt and was informed by the quilt teacher in front of the class that it was NOT a quilt, but a comforter. Yikes, 30 years later and I can still hear her say that in my head.