That doesn't seem that outlandish to me. I've had Dior transform 19 cm slim jeans into 17.5cm skinny jeans. They match the measurements.All you need to do is purchase the larger pair and have their tailor taper as you want. It may not be the perfect "look" however and yes you are taking a risk. Make sure you have a GREAT SA who will guide the tailor, because the tailor, let's face it, is far from a designer.