I see no problem with that strategy, honestly. The duvet cover often is the most expensive element in many instances. For example, I always recommend a linen canvas duvet cover since it's so damn durable and breathable out of all the fabric options available but it's insanely expensive ($500+ retail). This usually leaves little budget left over for a duvet insert for most people -- even when they find great deals at a few hundred dollars less from places like Ebay --- so it is not a new concept. I tend to also highly recommend silk inserts since they're great for hot sleepers and they are pretty reliable all-around (cheap ones to expensive ones). Hell, I have a cheap all-season silk insert from Costco (SilkHaven brand) that works really well for the price I paid for it, so buying budget-friendly duvet inserts sometimes is not a bad thing at all! The more expensive silk inserts tend to be either really nice outershell options or really high-end silk grades (6A) which raises the price quite a bit (but doesn't increase the breathability of the silk fill too much, overall). Overall, though, you'll probably do pretty well with a more average-priced insert as long as the filling material you're buying is breathable and decently durable. More on reddit.com

Big Lots or Home Goods first choice for recommendation…. Second choice: maybe TJ MAXX/Marshall’s More on reddit.com

I have a duvet from Casper that I really like. I bought it a few years ago so I don't recall the exact kind, but I believe it was supima cotton. Avoid their sateen products. Also, it may help to try something from a more basic brand. Check out Target. I've had bad experiences with pricer sheets and I continue to go back to my tried and true which is the Threshold sheets from Target. That may be the case for you and your duvet too. Also, it may help to wash your existing duvets multiple times. More on reddit.com

The duvet itself or a duvet cover? For the duvet itself, I've only ever spent a modest amount on them, I spend more on the covers. Personally, I'm not one who sleeps under duvets anyway; I usually take them off my bed before I go to sleep. I do love them for decorative purposes and have generally used the same trick that they use in design spaces which show off bedding setups: I buy two moderately-priced ones and double stuff my duvet cover. Makes it look super plush and luxurious. Super soft to lay on. I don't sleep under them anyway so I care more about the visual element. More on reddit.com