I found an image online (the closest approximation I could find) to give you a better idea. The set (a sofa/club chair) is in espresso leather with quite minimal features: with a narrow frame and subtle tacking detail. I wish I could share a pic of the furniture within the space, but we haven't moved in yet.

In as few words as possible, the space is a blank canvas. Very light, neutral tones.

Any ideas for a rug would be great too!

What are the colors of the walls, other seat, drapes?

as described in my previous post the chair and sofa are a set, both in espresso/dark brown leather.

The window coverings are nearly a non-factor as we have opted for retractable screens. No drapery.

As for the walls: Benjamin Moore PM-30 Bone White, with a feature wall painted in Timothy Straw (2149-40) flanking a beautifully restored, 100 year old, beam fireplace mantle.

I suppose the question is somewhat of a pandoras box. Now I find myself thinking, "I am sure they are going to want more details."

Here's a nice mix of color with brown leather. [https://www.houzz.com/photos/contemporary-family-room-contemporary-family-room-chicago-phvw-vp~193244[(https://www.houzz.com/photos/contemporary-family-room-contemporary-family-room-chicago-phvw-vp~193244)

Since absolutely everything you have described is a neutral perhaps you might want to go for a pattern on the third piece to bring some interest into the room.