So, it's 15 ft from window to fireplace? Is that the entry to the left of the fireplace in the last pic? That first pic Rawketgrl posted shows the seating area on an angle. That might work well in your room so that the piano and fireplace can be the focal points. An upholstered chair and table can to go on the end by the window. I like Acm's idea to bring in a game table, which can be just to display a few things if you want. The couch can be perpendicular to the fireplace, with the bookshelves behind it and couple of chairs facing the fireplace. Or, turned 90 so that the couch faces the fireplace. Chairs on one side, or both, depending on the room available. A table can be by the windows for display of some pretty things or used for games. Plants, tables w/ lamps to fill in the holes. A large rug will anchor your floating seating area. My combo family/living room is similar in size to yours. My seating area floats in the middle facing the fireplace, which is on the long wall. The back of my couch faces the entry because the shorter direction didn't give me enough room for my couch and tables. Around the perimeter is a huge lighted cabinet, a table with lamp, and two dressers that hold music/media with the tv on top.

Well, I was going to suggest the ubiquitous fiddle leaf fern, but looks like you have a cat, and they are toxic to cats. You might Google plants that are non-toxic to cats and see if anything grabs your interest. I think some palms may be ok with cats (and they can grow fairly large), or you might look for a contemporary plant stand and just sit a smaller plant on it -- maybe a giant tropical bromeliad or something along those lines. That said, if your cat is prone to pester plants, it's probably not a good idea to include one in your décor. (Definitely don't put a fake plant in this pretty space.)

Creating symmetry could help without adding a lot more items that could create a clutter vibe. You might consider rehanging the three octagon shelving pieces, one centered over each sofa cushion, placed to to form a slightly diagonal line with the smallest one at the high end and the add two new pieces -- higher over the left (aligned with where the first and second cushion meet) and lower than the diagonal line on the right (aligned where the middle and third cushion meet). Make these two newly added boxes or frames or decorative items of similar size and somehow relevant to each other, including the most dominant color. You could even add additional octagon shelving painted in your favorite bright or bold color.. https://www.etsy.com/listing/743522404/floating-geometric-octagon-shelf?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=octagon+shelf&ref=sr_gallery-1-8 You could choose two bold colored circles; https://www.etsy.com/listing/564205623/blue-agate-stone-design-circle-music?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_christmas_Art_and_Collectibles&utm_custom1=944d3c0c-df9a-4299-b772-94d6c8670b80&utm_content=go_1707294370_69268675129_331635229824_pla-314954651933_c__564205623&utm_custom2=1707294370&gclid=EAIaIQobChMIuc260cX46QIVGEmGCh01wg9FEAQYBSABEgJKv_D_BwE https://www.etsy.com/listing/564209897/colored-ocean-waves-falling-down-circle?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_christmas_Home_and_Living&utm_custom1=944d3c0c-df9a-4299-b772-94d6c8670b80&utm_content=go_1707294370_69268674649_331635229806_pla-303628061699_c__564209897&utm_custom2=1707294370&gclid=EAIaIQobChMIuc260cX46QIVGEmGCh01wg9FEAQYAiABEgIpPPD_BwE or add a different art form such as pressed metal wall art with pieces of similar size to each other. https://www.touchofclass.com/infinity-sun-wall-art-bronze/p/W842-001/?kc=ZMFPFS8&code=YMF03&color=Bronze&size=&tid=YMFPLA&gclid=EAIaIQobChMIw9PlwMT46QIVA2yGCh1xDAMjEAkYAiABEgLeO_D_BwE https://www.amazon.com/Contemporary-Artwork-Celtic-Handmade-Certified/dp/B0155G6JYO https://www.amazon.com/Urban-Designs-Handcrafted-Flock-Birds/dp/B0168873L6/ref=pd_lpo_201_img_0/136-9494044-5156007?_encoding=UTF8&pd_rd_i=B0168873L6&pd_rd_r=e390fd56-50ca-4460-a3e1-177ef7557f00&pd_rd_w=ezai0&pd_rd_wg=3Q8cq&pf_rd_p=7b36d496-f366-4631-94d3-61b87b52511b&pf_rd_r=6MXHM1EYMTEX2KNCS78G&psc=1&refRID=6MXHM1EYMTEX2KNCS78G https://www.amazon.com/Octagon-Octagonal-Hanging-Geometric-Decorative/dp/B07Q2MCNTR https://www.antiquefarmhouse.com/hand-carved-scalloped-wall-mirror.html https://www.amazon.com/dp/B07RHVZ33W/ref=sspa_dk_detail_0?psc=1&pd_rd_i=B07RHVZ33W&pd_rd_w=qYKx2&pf_rd_p=48d372c1-f7e1-4b8b-9d02-4bd86f5158c5&pd_rd_wg=h8EXz&pf_rd_r=G2S2W9Z4T4C442S6NW94&pd_rd_r=b919e319-2abf-412d-96cf-b1a6c589cb14&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExTVZZNDFISUdDQUkmZW5jcnlwdGVkSWQ9QTA0MTU0NzgzSjRXQzJJOVgxT0VVJmVuY3J5cHRlZEFkSWQ9QTAyNDgyMjg2Qk1QMElETlE1Nkwmd2lkZ2V0TmFtZT1zcF9kZXRhaWwmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl Mirrors wouldn't be my first choice but some people like them.

I’d cover them with slip covers. And get a larger rug. If your keeping it the red add a bigger rug and art. But think about what you’ll want to use in a future space also...