Your perfect jeans exist, I promise you - you just need to know what to look for | Jess CartnerMorley

Why is it so hard to buy jeans? You walk into a store where 2,458 almost identical pieces of blue denim are stacked in front of you. You approach this wall of denim and immediately a saleswoman barks CAN I HELP YOU? in a tone of voice you recognize as code, "I've spent all morning lining them up, lady, and if you lay your finger on my masterpiece, I'll put a curse on your unborn children. "

< p class="dcr-8zipgp">So of course being British you say "Oh no, I'm fine, thank you very much" and stare at the shelves trying to deduce obtuse names from the jeans - "Baxter", say, or "Houston" - which will magically make you look like Jane Birkin in St Tropez or Kate Moss in Glastonbury.

Labels on jeans are a bit like labels on wine bottles they are dense with geeky vocabulary that means absolutely nothing to the overwhelming majority of people who buy them. You just want to know which jeans will make your butt look nice / which bottle of red won't taste like vinegar or leave you poisoned for two days. When looking at a pair of jeans, the ounce weight of the fabric per yard is about as useful as the topographic details of the vineyard when choosing a bottle of wine.

But don't give up, because your perfect jeans are here, we promise. The great thing about jeans is that there is no single, exclusive, expensive iteration that is the perfect jean. It's the quintessential democratic fashion item. The best jeans aren't in a more expensive fabric – cashmere isn't a plus here – and they're never, ever upgraded with logos or glittery bits. All that really matters is size, leg shape and degree of stretch.

Elizabeth Radcliffe is Levi's master tailor, and if you've got £750 to spare, she'll bring his Savile Row training to create bespoke jeans in his Soho studio just for you. She probably knows more about the fits and tricks that make jeans work than anyone else, and a while ago I spent an enlightening half hour trying on jeans with her and downloading its wisdom to share it with you.

It turns out that the most flattering waistline, for me and for many women, is neither a low waist nor a ribbed high waist, but one that sits about an inch below the belly button in the front and curves up and down the sides to sit slightly higher in the back, so that it clings to your hips and doesn't stay gaping. Also, medium to heavyweight denim works best for most women, with just enough volume so the figure can hug a curve, but enough structure to cinch around your waist. And I learned that the lowest point of the back pocket should be slightly above the crease at the top of the leg, to create a visual distinction between the bottom and the thigh.

Lizzie had me sit and stand, shoes on and off, hem up or down, to determine which shape and leg length worked best. I prefer jeans that come off the leg, so straight styles work for me; if you like denim that hugs your shape, you'll want a skinny or a bootcut.

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Dressing on and off in locker rooms isn't a fun idea, but there's no shortcuts. Try as many pairs as possible. Oh, and don't worry about size. My favorite pair of jeans are a vintage pair of 501s from the 1990s. The waistline on this tag is three inches larger than an identically sized pair of jeans purchased recently. Modern vanity sizing in action, you see: brands have figured out that if a customer fits a size smaller than she expects, she'll be delighted and therefore inclined to buy. It's silly on all fronts, so please don't fall for it. Don't look at the size tag, look in the mirror. Twenty minutes in the locker room is all that separates you from your jeans forever. Dedicate time now and they will pay you back for the next 20 years.