1. A high thread count is not as important as you think.
It's easy to find luxury 1,500-thread-count sheets at bargain prices. But buyer beware: Thread count (the number of fibers per square inch) isn't a sign of quality, since manufacturers can boost the count using thin, low-quality strands that don't hold up well to washing. A sheet like the Martha Stewart Collection 360 Thread Count Percale (macys.com; from $50) can feel equally luxurious; be wary of any with a thread count over 400.
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2. Look for long-staple cotton.
With fibers longer than 1 1/8 inches, long-staple cotton is more durable, softer, and less likely to pill than sheets made from inferior short-staple stuff. Extra-long staple (longer than 1 3/8 inches), like the fibers found in Garnet Hill's Hemstitched Supima Percale Bedding (garnethill.com; from $38), fares even better over time.
3. Try these new online linen sellers.
Like the mattressmakers, a number of start-ups are focused on selling a limited range of high-end sheets directly to customers online, eliminating a few steps (and markups) in the traditional supply chain. We like Classic Core Set from Brooklinen in long-staple Egyptian cotton, pictured above, (brooklinen.com; from $99). L.A.-based Parachute manufactures its long-staple cotton sheets in Tuscany (parachutehome.com; sets from $89), while Boll & Branch sells organic-cotton sateen sheet sets from $200 (bollandbranch.com). All offer 30-day returns.
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4. And don't skimp on your duvet.
Now that you have the sheet-buying game down, here's what you should keep in mind if you're in the market for a new duvet. The best ones are carefully constructed to provide warmth even after years of use (and washings). It's one piece of bedding where you get what you pay for. Here, we picked two of our favorites.
The All-Around Pick
The Parachute Home Down Duvet has all the qualities you should seek in a down duvet. A high fill-power of 750 gives it warmth, loftiness, and a light weight (25 oz); baffle-box construction ensures that the down fill won't shift and lump up, leaving you with cold spots. As with all down duvets, use a cotton slipcover to prolong its life. [$389 for queen size; parachutehome.com]
The Subzero Pick
Whether you sleep in a drafty mountain home, want to save on heating bills, or just enjoy a cracked window when you sleep (even in January), the over-the-top-toasty Feathered Friends Baffled Box Ultimate 700 should be your choice. The Seattle outfitter backs the duvet with a lifetime guarantee; they'll wash or repair it, too. [$459 for a 38-oz full size; featheredfriends.com]