I like the simplicity of what you already have, and wonder if velvet wouldn't look too heavy in warmer seasons. I would choose a heavier material with perhaps a self pattern in either white or cream, and splurge on a beautiful rug and great art instead.

Pretty room!

Try Country Curtains for curtain rods, they're having a going out of business sale, and have very good quality.

Do you need a double rod? For example, for sheers if privacy or glare is a concern? Otherwise, I'd go with a single rod for simplicity's sake. I like black or wrought iron, which is a nice and easy way to make use of the standard decorating advice to have some black somewhere in the room.

I think velvet would look lovely during the cooler/colder part of the year, depending on where you live. And with the color paint you've chosen, any color except for the brown family (beige/taupe/tan etc), would work. Do you want a solid color or pattern? You could go with linen curtains in the spring and summer; Ikea's Aina linen curtains are inexpensive and sold by the pair in a variety of colors (white, grey, blue). Besides Country Curtains, Anthro, Pottery Barn, and Ikea, I would also take a look at Ballard Designs for curtains (including velvet) and hardware.

Be sure to pull out the curtain rods as far as they can go so when the curtains are open, they're not blocking the window at all, for maximum light in the room. I've found this is a helpful blog post,

https://fredgonsowskigardenhome.com/2011/05/03/the-right-way-to-hang-curtains-and-drapes/

https://www.halfpricedrapes.com/length/120/1724/signature-silk-curtains.html?sort=

You may want to look at the above site. They have 100" width panels in many of their curtains and up to 120" long that are not custom. They do have some very, very light gray tones that almost look off white on the monitor. I'd select a fabric that isn't too heavy personally, but if you like velvet they do have it as well and you can order free swatches which is a good option.

Good luck.

Might I suggest a layered look?

Mount the drapery up HIGH, to create height and bring the eye up. A darker hardware will be BOLD and oh so sassy. Layer a woven woven Roman shade underneath and the amount of privacy/light control is superb.

Using a light linen-like fabric for the drapery brings a whimsy vibe to your space.

Or perhaps, a textured roller shade with opaque fabric for the drapery.

I do like the oh-so-sassy-whimsy-vibe of Gordon's top pic, but then I'm a sucker for bamboo matchstick blinds and oh so sassy dark hardware : )

Thank you Becky!! ;)