Your fireplace stone is just perfect! So as overall furniture disposure. I would take away the chair pattern away, so as the big picture above the fireplace - removing it brings an an clear empty horizontal line into the space (picture hanging too high fill the space too much). I would remove the things from the top of furniture away, so as change lampshade into desired beige and ... place the same one to the other side - in order to properly close symmetrical outlook.

Whatever window treatment you use, it should be the same as the next room if possible - in order to be consistent with the next room or in interior overall.

If you paint the black furniture to white, I would paint the fireplace shelf also. and bring big new white table - maybe with some seaside feeling (e.g. with our inside).

If you cover your FP with a surround/mantel as in your second inspiration, it will be more formal looking. A lot of the stone pattern will go away, so you can use pattern on the flanking chairs. For paint, I like Ben Moore's Sea Salt or Sea Cliff Heights, but paint shouldn't be selected until the fabrics and upholstery are chosen, so delay that decision and work on the new furniture first.

sea salt CSP-95 · More Info

Seacliff Heights 688 Paint · More Info

It would be easy just to paint the mantel white on the FP - but you'll definitely want the stone texture and color with your new palette.

I think the black will actually make a beautiful accent to the color palette in the pictures you posted. Consider that as a component when selecting fabric for the windows and I think you can incorporate that into your tranquil scheme.

Can you add another photo of the adjoining spaces? Looks like your chairs are black or dark stained? Window treatments are just a valance?

I love your second inspiration picture. Love the way the value chairs really make the fireplace a focal point. As lovely as having nearly everything the same color, I find some things get lost.

Thank you for all of your wonderful comments. A big help! I love my fireplace, too. The mantel was custom made of reclaimed wood and stained, so I will keep. Good to know about keeping the patterns away from the stone. I agree and love the thoughts on color and changes on accessories/symmetry. My kitchen chairs and barstools are black, which I may or may not paint, too. The valance in the adjoining room is old and will definitely be going.