Are you sure it's 91" long. Looks closer to 50"

https://www.amazon.com/YWAMZDZ-Cushions-Waterproof-Anti-cat-Furniture/dp/B0CWPDFZ11?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A2N290NKIMSO4Z&gQT=1

Simple project for a local upholstery shop. Choose your own fabric.

Looks much samller than 90" so maybe recheck that but any upholstwrry shop caan do this in fact if you can swe you could do this in a day To be honest I would not have anyone sitting there in a space with windows right behind I would use thet spat for some nice happy plants Seems to be alot of tiny shelves what is it you plan to put on those ? I like window seats but not where I can lean back and break a window

I've had good luck with customcushions.com

It's a very nice space and looks like quality workmanship. I have one just like that and it's in a back hallway--I use it to sit down to take shoes/boots on and off. It's not a space where you sit and lounge, but with cushions and some pillows it is very pretty.

I usually will have the cushions custom made by an upholstery shop or a seamstress who makes curtains and pillows.

I’m reading it to mean that the picture shown is not the actual one, but an example.

Etsy is another source for custom window seat cushions.

I had one made for my mudroom by a local upholstery shop. I picked the fabric, size and foam quality. I used an indoor/outdoor fabric for maximum durability.

Hi Jilly, I misread the original post. Didn't realize that the photo was not the OP's window seat.

I could be wrong, Diana … just saw the Pinterest ”Save” tag and she said ”something like this”. I figured it was inspo she saved from Pinterest. :)

If it truly is 90 you might look for two 45” long standard cushions. Get thick, substantial cushions. Choose durable fabric like a Sunbrella. Get zippers for removal and cleaning. Quality is the key. I suggest custom. Get them made once, and correctly.

Just another vote for Etsy