I think sheer curtains would dress it up a bit, without being overly heavy

I'd do stationary panels on either end, just to soften it a bit. You'd likely have to move your wall shelves over a bit to accommodate the panel.

Stationary drapery panels with woven wood shades · More Info

Linen panels would be a good choice. Ikea has some very nice ones at a reasonable cost.

It doesn’t really look like there is room for curtains

Personally I love the clean look but panel on each side would look nice.