That collar idea is a really good one. And it would be fairly easy. To do that take off the original collar, use it as a pattern and extend the top edge out to a fold-able length. Sew it as you would do any collar and then sew it back on the coat. The lapel part under the collar would probably need a button to close it snug around your neck. You can also put buttons along the edge of the new collar.
You could also make a belt to spice it up. That's what I've been doing for some of the coats I make and sell... here's an example