Second on the Costco duvet - or look up comforter instead. Costco is just great in general. Also, check out HomeGoods. I don't know your design preferences, but here is a gorgeous linen/cotton duvet cover for $59. You can put a Costco down and feather duvet in it for $55 (the pillows of the same design are good - I've had them - no prickliness). Here's a white herringbone cotton set , made in Portugal - or blue navy . Here's blue flannel , if that's your thing. Here's a plain polyester comforter. . Or here's a down one by a good brand. Here's a Costco duvet set though I'd go wool later, for more warmth. Down is cheaper for warmth, if you are not allergic. Or here is an all-cotton comforter . Or look at Quince.com - ethically lower costs, and they will guarantee their products. They have a bundle with sheets included , but you'd have to add the duvet insert. This is a duvet and comforter in one quilt. More on reddit.com

I think these look more like comforters and not duvets. Laura Ashley has a very similar feel to these, and has both comforters and duvet covers. https://www.lauraashleyusa.com/pages/bedding More on reddit.com

You'll have to check the actual dimensions either way, because there's no standard sizing across the industry. One brand's king size can be very different than another's. California King is a bit narrower and longer than a regular King. Quite often they only differ by about 2" on all sides, so they can fit into each others' covers fairly well. More on reddit.com

This is a Fakespot Reviews Analysis bot. Fakespot detects fake reviews, fake products and unreliable sellers using AI. Here is the analysis for the Amazon product reviews: Name: Since Silk All-Season Silk Comforter, White Silk Duvet for Night Sweats Hot Sleepers，100% Long Strand Mulberry Silk, 100% Cotton Duvet Cover(Queen(90-86in)) Company: Visit the Since Silk Store Amazon Product Rating: 4.4 Fakespot Reviews Grade: F Adjusted Fakespot Rating: Insufficient reliable reviews Analysis Performed at: 11-10-2023 Link to Fakespot Analysis | Check out the Fakespot Chrome Extension! Fakespot analyzes the reviews authenticity and not the product quality using AI. We look for real reviews that mention product issues such as counterfeits, defects, and bad return policies that fake reviews try to hide from consumers. We give an A-F letter for trustworthiness of reviews. A = very trustworthy reviews, F = highly untrustworthy reviews. We also provide seller ratings to warn you if the seller can be trusted or not. More on reddit.com