It was my "look" a couple of years ago, but I didn't actually buy any Sezane - I hunted down very similar items on Ebay from M&S and other places, and did it for a fraction of the price. There was a cerise cashmere cardigan for about a million pounds, for instance, and I got what I strongly suspect was a better quality one on ebay for about £25, new with tags, from M&S.
I have one silk shirt from there, which is lovely, but I'm afraid to wash it.
Honestly, if you see an outfit you really like on Sezane, deconstruct what you like about it (apart from the rake thin model with perfect skin in a gorgeous location), and I BET you could put it together from M&S and a dash of & Other Stories. Open a few more buttons than you would normally and wear some long gold necklaces showing through underneath.
It's very much styling over substance!
Also, realistically speaking, a lot of what makes the website look cool is the plethora of slim 25 year olds wearing those lovely jumpers and blouses with short skirts and bare, tanned legs, and while your lifestyle might be very different from mine, I'm not sure I could be doing with bare legs & a mini out and about on a day like today, even with a bottle of St Tropez, just to make my jumpers look snazzier.