Westfield London, Shepherds Bush. 9.15am on a chilly, rainy, grey morning. The shopping centre is empty and I’m being let into the Donna Ida boutique by the woman herself. ‘Look, don’t worry,’ she says, ‘It’s going to be fine. The right pair of jeans for you does exist, you just haven’t met them yet.’

‘But you don’t understand,’ I tell her grumpily, ‘I spent two-and-a-half hours in a big department store with a sales assistant who is now in therapy after failing to help me in my quest. He was on the phone to the Samaritans when I left empty-handed.’

‘It’s going to be fine,’ she says again, cleverly ignoring my whining and patiently leading me past shelf upon shelf of jeans and a row of neatly rolled knickers called Hanky Panky (more of them later).

The designer Yves Saint Laurent once said: ‘I wish I had invented blue jeans. They have expression, modesty, sex appeal, simplicity – all I hope for in my clothes.’ But how can something so simple be so damn difficult to buy I wonder?

I’m at Donna Ida because I only have two pairs of jeans. I donated the rest to charity after the birth of baby Mabel last year, when I realised the super-tight skinny jean was no longer the right ‘look’ for an editor in chief and mother of four. So every weekend for months, I’ve been staring at the gap in the wardrobe where my closet staple should be. How foolish. But who better to sort me out than Donna. What she doesn’t know about shape, size, fit, brand, texture, trend and stretch isn’t worth knowing.

‘Make friends with these,’ she says, handing me a pile and encouraging me to go down a size from the one I normally buy and, more crucially, to consider ‘high-waisted’ designs.

Donna, a glamorous down-to-earth Aussie with a practical air, has four boutiques and runs a denim clinic. All her staff are advised on how to find the best fit for every customer. You have to let them talk you through it, though, and be open-minded about the styles they offer – which is a new way of thinking for me. She stocks 24 brands, from J Brand to Stella McCartney, and she uses the words ‘muffin top’, which reassured me no end.

Her advice, as I tried on pair after pair, is to look out for a crease at the front around the crotch area (you don’t want one) and if you can get your hand in the back they are too big. All jeans give over time, she adds. My problem was going for a too low-waisted jean and trying on a denim that was too soft – I needed more structure. She also made me get a belt (we opted for one we called ‘the Jennifer Aniston belt’ – a brown leather one that you wear with boyfriend jeans in the manner of JA, who curiously always wears a belt with her jeans).

After an hour and a half, I am standing in front of the till with five pairs of jeans in my hand – a denim wardrobe. Not bad to start from scratch and have every denim need catered for that quickly. And no one cried either. Unlike last time.

This is what I got:

Current/Elliott Boyfriend Jeans in Loved, £240: for weekends, worn with the belt and big, baggy jumpers or white tees. You can roll the bottom if necessary.

J Brand 811 Skinny Jeans in Ignite, £225. Smart skinnies in a dark blue.

Paige Skyline Ankle Peg Jeans in black, £195: You need black for work and home.

J Brand Kori Jeans in Pure, £210: Short length and tapered – modern but classic, too. I’ve worn these to work.

MiH Jeans Paris Crop Jean in white, £145: A stronger denim for white as it isn’t as forgiving on the leg as soft denim.

Denim Wash, £20: Always use a specific denim cleaner and don’t wash jeans too often.

Hanky Panky briefs in black, from £17 to £26 – I will not be blogging with a picture of me in these, just FYI.

And I’ve put an order in for the J Brand Major in Vintage Armadillo because this combat colour is perfect with black V-necks for a quick weekend wear.

I avoided neons as I have one pair of yellow J Brands at home, but there are plenty of pastels, fluoros and print to choose from this season. So there you have it. This is a basic denim selection for a slimmish woman of around 5ft 3in with issues about showing too much thigh.

Donna believes you need around five pairs to rotate for every moment in your life. And if you are curvy, she thinks the key to wearing denim is to stick to styles that flatter your natural shape rather than detracts from it, choosing styles with plenty of structure and just a little bit of give. Straight-leg styles helpfully elongate the leg, while jeans made of heavy-weight denim have a small amount of stretch. For the more shapely woman, add these brands to your list this season:

Goldsign Quinn Slim Bootcut Jeans in Owena, £225

Hudson Beth Baby Bootcut Jeans in I Want To, £215

J Brand 814 Straight leg Jean in Pure, £190

James Jeans Hunter Straight Leg Jeans in Tempest, £200

Paige Laguna Bootcut Jeans in Clarity £170

The fashion team advise me that the on-trend jeans to look for this season are straight-leg, non-stretch denim similar to old Levi’s, often worn with a turn-up or a slight crop to suit the cropped trouser trend. Topshop has a great version of old Levi’s we like.

Christopher Kane has done a second collaboration with J Brand for a/w 2012 that offers a quite wide-legged, almost skater-girl style. And skinny jeans are still everywhere, worn slouchy, aka Balmain and Isabel Marant. They were very much present at this week’s press days for the new season.

Generally, there is a move away from stretch denim to a heavier, classic denim. So now you know. It really is worth taking a morning to find the right pair or pairs for a denim wardrobe because you wear them a lot and they are the easiest and quickest piece to dress up or down.

Has this been helpful? I think it was. What fashion or shopping dilemma shall we tackle next? Over to you – and don’t mention peplums, you all know how I feel about them.

http://www.donnaida.com/denim-clinic.html