It is a very dark space to be adding heavy dark velvet. Do you have a peeping Tom who hangs out on the porch? Can passers-by see in? You really do need some lamps, unless the cat will destroy them.

Yes we are on a busy street ..cars and people walk by all hours.. but cats love to sit and watch...I hate having blinds open for anyone to c in... Having curtains would give some privacy and still allow them to c out... We have recessed lights running the ceiling , not on in photo.

I like your ideas. Nice style! Measure the space you have on each side of the window and the door. The curtains need to stack back off the glass as much as possible to keep the room from being darker. Do you use the fireplace?

Looks like a great space with a lot of potential for some nice window treatments. Horizontal blinds like that were never meant to go over a sliding door for the same reasons you don't like them. Hunter Douglas offers various lines of window coverings that come in both a horizontal and vertical version so you could match same fabric/colors but different orientations for the window vs. the door. I would recommend check out Designer Roller Shades & Skyline Gliding Panels or Duette Honeycomb Shades with Vertiglide.

Recessed lights are general purpose lighting, but to create an intimate space you need table, floor and accent lights as well. Overhead lighting isn't flattering to people either. I agree that drapes and that corner fireplace together are a hazard.

I would do some simple roller shades on the slider since you said they are up most of the time. Then I would do a fabric cornice in the space above the door, basically from the top of the door to the ceiling, maybe in a pattern that would pick up the blue from the other room.