Wanted: A Hat

It's Tutorial-to-Try Tuesday.  I haven't found a tutorial yet for what I want to make.  As a confirmed bun-wearer, I find that it is not that easy to find hats that fit over or around the bun.

I was watching Coco before Chanel and noticed that in the old days, they used hatpins to "attach" the hat to the head.  You end up with the hat perched on top of the head like a showpiece which isn't quite what I want.  I'm more interested in keeping my ears warm in the cold.

I have 2 hats which work: one is just a regular hat, but I got a bigger size so it can cover the bun (and my ears) but just barely.  The other is one of those knit equestrian-looking hats with a small brim.  It's stretchy.

It does work well, but you get a bit of a bump at the back, which Big J says is not really noticeable. 

I think there must be a way to refashion a hat out of a sweater.  Something similar to this:

Then the bun could just be covered by that extra bit at the bottom.

I can almost picture how to do it.  The waist band of the sweater (or perhaps the neck?) would be used to make the hat band which goes around the head.  I'm just not sure how the rest of it would be done.  Maybe use a kid's sweater?  Can anyone point me to a tutorial?