Hi there...
I've never had a problem with just doing the knots..never quilted or tied and never had a problem with the layers separating - I think it may be something about the fleece on fleece that keeps them kind of together...
They do make up really well and are a lot of fun to do.
I done a lot of these..even though I've done a lot of the larger ones the more recent ones I've done are about 36" square for babies.....they make great baby gifts....