The key thing to think about is making sure the 2 sofas are different enough that it doesn't look like you tried to match them and failed. You want to make sure the shape of the arms is in the same style - rounded or square? do they go to the front edge of the seats or not? Also is the back a tight back or loose cushions? Make sure the new sofa has the same visual weight as the old one. If it's a heavy looking sofa, get another heavy looking sofa. Since the leather one is black, I'd go with a grey colour. It will look good with what you have and be easy to clean. Make sure the fabric is 100% polyester. That is more durable than fabrics with cotton in them.

UGH im going through the same thing. My household consists of 2 cats (one is a kitten who is hyper 24/7) a husband who plops down on everything, and eats anything he can while sitting on the sofa, a 60 lb german shepherd standard poodle mix that sheds like no other, and a 4 year old who spills, draws, puts make up on anything in sight! We are switching to leather. Its a lot more durable, so much easier to clean, the upkeep on a linen sofa is too much to handle, by the time I get done cleaning it, another stain is made! It also shows wear and tear a little too much. Have you thought about having a custom made cover? that way you can get the leather couch and then if you start to reallllly miss that linen put the cover on! I am personally a fan of pure white couches, and the sectional we are looking at is also a dark brown leather. I will be purchasing the sectional and also having a slip cover custom made so when I am feeling a little like I want a different texture for the furniture I can easily just slip that on.

just giving some opinion here. it would definitely look great with some cushions on it. Would recommend you to get from an cushion online retailer in Singapore called 1001cushion My favorite cushion from them is Garden Cushion & Metallic Cushion (Classy and Fresh) P/S: They are doing promotion of FREE shipping now.

I'm not sure if there are any hard and fast rules but I think it needs to be probably at least half the width of the sofa to look good. In your case I would probably go for something 65-75% of the width of the sofa with maybe the height around 55-70% of the length. You could also try a large portrait style, the best thing to do is to cut out a template and hang it on the wall to see what you like as chesterfields are normally quite low. I'd also move the sofa slightly but are the ceiling lights positioned over the sofa? Hard to tell from the camera angle. I also thought of the Vintage film pics but maybe not original. My basement has a slight film theme with lighting ( actually I have a Chesterfield and cowhide too!) and I have large black and white pics of movie stars but not from film clips ie the iconic Michael Caine shot taken by David Bailey. I also love vintage travel posters, I know they've been around for quite a while now but you could find a destination that means something to you. Or look at industriał style art with a pop of colour. Or an abstract with pops of colour.