Cuddledown, the Company Store, Garnet Hill and Lands' end make soft, high quality covers that last for years and years. However, I will not pay their regular prices. Sales, clearance and coupon codes bring them way down and they become, to me, a good deal. The only duvet covers I have not been happy with are Target and Ikea. Best I ever got and has lasted 13 yrs and is still luxurious, is one from Peacock Alley, very expensive brand that is occasionally found at Tuesday Morning stores and Sierra Trading Post online. Their sheets are amazing. If you can find Peacock Alley in your price range, scoop it up, definitely worth it.
Cuddledown's duvets are IMHO the best, last forever, down doesn't shift, lofty. They too, can be found on sale, clearance, coupon codes, etc, bringing very good duvets down to department store pricing. They have outlets in Maine and I can't remember, I believe NH, if you are anywhere near there, best prices.
this makes me sound very picky about bedding, lol. I got spoiled by visiting a Cuddledown outlet decades ago and it's hard to go back, buying not so hot stuff, that if I wait, a good deal will come along on other websites