If you want a more casual looking coat, how about the more modern cocoon shaped coats that are around at the moment? I made a Burda one a little while back and I wear it a lot, or as much as one can wear a coat at the moment. I wasn't sure that I'd be able to grade it for my pear shape, but I got away with it (at least 2 or 3 sizes bigger at the hip than the shoulder) and it's very comfy. I posted about it
here.
I've also got another new coat on the go, but it's waiting for the right lining to come along; again, it's a Burda pattern and, again, more cocoon shaped and using giant snaps rather than buttons, details
here.
I agree with
@Renegade Sewist that the more traditional notched collar design looks better with structure; I think without the necessary underpinnings, it just looks badly made. The slouchy part comes from how you style it more than how it's made, I tend to think.
Stylearc have lots of slouchy coats - I have their
Parker coat pattern, which is a fabulous slouchy, casual coat and a modern interpretation of a notched collar. The patch pockets give it a more casual look, too, and there's enough going on that it doesn't really emphasise hip width.
I just love a new coat.