Katie is wearing size 5 trousers and size 4 jacket.

Height:  5'6 / 169cm
Chest: 44.5" / 113cm
Waist at bellybutton: 41" / 104cm
Hips around bottom: 52" / 133cm

In the majority of brands Katie is a size UK20. She wears M&S jeans in 20, or Lucy&Yak in 36 (because they are "big bum, fitted waist" style, so I can size down from their recommended women's dress size comparison). I'm between 18/20 on top, 36F, and wear size M/L in unisex t-shirts. My general problem with trousers and skirts is that if they fit my thighs and bum, the waist is massive. To fit my waist, I won't be able to get them over my knees, or the rise isn't long enough to allow for my belly / bum, so high waisted stuff ends up not being high waisted enough. Also tops often size up the body , but not the arm circumference. And also generally larger top sizes don't allow for larger boobs being positioned lower. 

With my ISP trousers, the size 5 and up have a larger front rise, and also a gusset, and the waistband can be cinched in, and still look great over my bum. There is plenty of room in the boxy shape of the jacket for my boobs, and arm circumference. I love wearing them 'jumpsuit style'!