I think if you get separate cushions they will slide around. One cushion will look better.

You shouldn't need to take it off that often unless your dog has very dirty paws.

In which case, I would train him to let you wash his paws when he comes in the house.

Yes, that can be done.

We have one long cushion on ours but it's in the guest bedroom and doesn't get a lot of use. I've recovered it once in 30 years.

It would be nice if you can make it so you can flip it and use both sides. You might also want to add something grippy underneath so your dog doesn’t pull it off when getting on. If you use outdoor cushions you can just take it outside and wash it with hose and bucket.

I have one long one. The cover is removable and machine washable. Have not had wash it yet. I just spot clean and vacuum as needed..

My daughter did her window seat in sections because she has pull out cabinets in the center which she moves to the other side of the room so she has Christmas tree space. Plus foam is cheaper in smaller sections....lol....she is a diyer.......either way works I think.

Wouldn't one pet bed work where he/she likes to be? I say that partly cause there are little visuals already, with vent, etc... a thought.

First off, lovely room with great architectural features!

That is quite a large window seat--exactly how long is it? I have 3 window seats, all with one cushion, the largest is 70" long. It's bulky, but I don't move it much. If you're going to go with more than one, you probably should do three, to match up with the drawers and heater below. I'd probably go with one, and have it made to fit snugly.

Unless you create a case for the filling and stuff it with shredded foam or some other type of material, you might have a hard time finding a 10ft piece of foam unless it is a special order.

Even mattress toppers are not 10ft. long. A cushion filled with resilient foam and wrapped in polyester might be like dragging around a dead body. Just something to consider.

If the cushion is one piece, consider that you will need to railroad your fabric to avoid having seams on the face of the cushion.

https://www.cushionsource.com/buy-cushions.php?type=window

etsy source

Make sure any toss pillows used to anchor the ends should be about 26x26 to provide some support

One would look great but I’m thinking when someone sits in the middle the two sides flop up. Lol. Anyways agreed with the above to do a grip on bottom

I suggest you make sure it’s got the same fabric on the bottom and the symmetrical side to side so you can flip it over. That will help extend its wear

For my window seat I wrapped the fabric around foam so there was only one seam along the back. Suggest using a zipper or Velcro so you can remove to wash. The bench looks like it could be too narrow to sit on if cushions were added for back support.

We have a dog and two cats and I eventually removed the padded seating. I find cushions are enough and since it’s rare anyone sits there, it doesn’t have to be comfy. Normally I have more back cushions (+ one for the cats) and it works well visually and pet wise.

Your window seat is long so try adding 3 or 4 cushions on each end and a washable dog bed that can be removed when necessary and see what you think, based on your needs. Love the last picture 😀