I only use down inserts. They are available many places, even Amazon. Check around for prices. Some fabric stores also carry them.

I buy all my down inserts from Crate & Barrel. Great quality and price.

Down, unless one is allergic.

But….kitchen bench throw pillows that will be moved whenever someone sits there —-what? I would re- think that. Sounds so clutter- y. Sure, for even a useful throw pillow, not everyone likes a pillow, depending on depth of seating and preferences. That’s why it’s good to only have 1or 2 on a sofa and avoid these stagey photo shoots of 2-3 layered pillows. Is the bench backless, or wood, or have a seat or back cushion? Is the bench almost never used, so that you feel if makes sense to have pillows there for “ looks” because you see it every day ? Snd I do see how fabric, color, pattern can create a nice decorative- only view, like styling a formal DR table top or buffet, then moving all that for occasional dinners.

If the pillows are never used at all, you have more options. For my down pillows, I don’t routinely overstuff my inserts because I think it can make pillows too firm for good malleability, which I want for squishy comfort. But lot of people like the “ look” of the fat pillow and ding plan for anyone to use it.

I use a feather down combo insert. The ARC thrift store usually has tons of donated pillows for $3.50. I take out the inserts. I have a LOT of pillows. The almost free price is awesome.

If Pottery Barn has pure white down inserts....I've never seen or heard of one.

If they're purely decorative, then perhaps polyfill would be sufficient? Chain retailers like Michael's, Joann Fabrics and Walmart sell those.

My pillows are decorative, but i personally think down looks better than polyfill. But the stores you mentioned will have all of those.

To the OP, another tip, buy an insert larger than the cover.

These get rave reviews from a FB group I participate in. Pillow inserts

Thanks everyone for your suggestions. The bench is under a bank of windows and is the main focal point of the kitchen. It is a 10 ft old church pew painted white.... so we see a straight blah back under the windows. We rarely use the bench except when having a crowd over, so the thinking is to drop a few nice pillows in to spice up the view and bring in some colors from the surrounding rooms. I'm not a big fan of loading up sofas and beds that only need to be moved... but I think it makes sense in this situation.