I would go with one piece.

One long cushion

One long cushions and some decorative pillows

Ok.... I understand why everyone said one long cushion! But.... 1-10 ft long cushion will not keep its shape! You will need to tuft the top so the foam will keep a firmer top! Better yet, I would tough both sides so you could flip the cushions! I agree by adding throw pillows!!

I think I would go with two cushions. I think it would look a little friendlier, cottagier (is there a word?) And, I think the tufting would be practical, but, I think I would not tuft. I like the simplier look. Perhaps, I am just contrary tonight :o) Hope not!

I think 2 five foot cushions would be fine. For wear pattern you would have more flexibility, they can be flipped side to side and top to bottom, think about using a sunbrella fabric great for fad resistance and spills

I would do two or maybe four flat foam cushions and have piping around the edges. How about roll cushions at either end? As well as scatter cushions.

One long one, but be sure it is thick enough, I recommend 4 with a somewhat firm foam and dacron wrap. Most workrooms make them too thin.

I meant 4" thick.

I would go with two and rolled tufted pillows at the ends and contrasting throw pillows

As a custom workroom, I agree with two cushions on the bottom. They will maintain the shape better.

Definitely two cushions which would also compliment the paneling on the front of the seat which is in two distinct pieces. Definitely a bolster cushion ( log roll) on each end and then a combination of scatters in between. And yes, wrap the foam in Dacron to give it a more rounded feel than totally square.

I have very long cushions and they don't wear well. Definitely use sunbrella fabric and test thickness. Mine are too thin and custom.

I know this is a very old post, but I too am looking for advise on one vs. two cushions on our window seat. We actually will have two window seats, each about 9 feet long. The windows are similar to your picture, so I am wondering what you ending up doing, if you’re happy with it and if you have any pictures. Thanks!

What a great idea, the pics are beautiful! Would have never thought of using a mattress! Thank for sharing!

Very happy with our 2 cushions They have held their shape all these years well. We have a storage space underneath the cushions and having 2 cushions is MUCH better if you have a storage space underneath because you can easily tip them up onto either side to access the storage underneath, or you can swing one out or up to access the space underneath. If we had one mattress, that would have been much more unwieldy. Also, if you have 1 cushion and 1 cover and it gets a stain, then you can only flip it once and you are done, and the entire cover is ruined. With 2, you can flip 4 stains (2 on each pillow)! Hope that makes sense. I can take a photo if you like, tomorrow in daylight.

Thank you so much for your insight, some very good points! I would LOVE to see a picture!

rick12345, your comment reminded me of something. When we went to pick the mattress up, the company made a mistake, and accidentally made 2 half mattresses instead of one long one. They were so nice about it. When we went back the following week we ended up with the 93” mattress plus the two 46.5” each mattresses. They said they couldn’t sell them so we might as well take them. We store them inside underneath the seat. This settee is kind of overflow sleeping area for company (pre covid). That’s why I wanted one long mattress.

I just took 2 photos -- hard to believe we did this remodel 7 years ago! Hope these are helpful.

Looks great! Is there a little lip on the front edge to hold the cushions on? If not, do they tend to slip around? On an unrelated note, I have to decide whether I want small lights on the side walls, I see you don’t have them, do you ever wish you did? Thank you so much for your pics and thoughts!

No lip but it's mostly the dogs who sit up there! Anytime anyone ever sits there, though, I never noticed any slipping and I could see that being annoying! On lights, it would be nice if you sat there to read and it was a deep enough window seat to sleep in!