I am looking for interesting header detail for my curtains

I just make a plywood valance over mine in the bedroom. I have the Light sheers on a slider rod, the curtains on a Grommet and Pole drape with the valance of material matching the custom quilt on the bed and it looks charming.

How about big wooden corbels? Lowe's and Home Depot have several styles, then you stain or paint them as you want. Best wishes 😇

If you want something easy to change out (patterns, colors, edging, etc. https://www.youtube.com/watch?v=ScNihbvjJtQ

Try Pinterest for a multitude of ideas

...https://www.pinterest.com/explore/window-valances

Tell us a bit about the style of your house.

You might be interested in going on the blog "Stone Gable" and see what she did with some plain curtains. She covers many, many topics but just look for where she talks about "curtains for her family room". You might like it. Of course, like Suellen Hintz (above) is asking ... a lot depends on your personal decor! A good source, too, is Pinterest.

How about a cornice? Here are a couple links.

https://www.pinterest.com/explore/cornices/

https://www.houzz.com/upholstered-cornice-ideas

Maybe a valence? Frame out in wood, upholster in matching or contrasting fabric

First off, what's a header? I once used wire to hold a mass of faux flower bouquets on my curtain rod. Thought it up all by myself. My most proudest accomplishment, seeing as I have the same level of artsy creativity as a brick