I'm now on my third pair of Tikiboo leggings (not a sponsored post but is a referral link) so I thought I'd share my thoughts on the fit, as all three of mine are different sizes/fit.
Firstly, they are thick, and perfectly good for squats and bending over. You barely see a knicker line either. So that's good to know.
They either come as a standard waist, or high/zip (higher waist with a zip pocket). I wasn't sure about size either, so in my first order, I ordered one pair which was a size Medium, and High Waist, and the second was size Small and Standard waist. It's sod's law, that of course I realised that what I actually needed was a size Small with a High Waist. I have a pronounced difference between my waist and my hips (I have a small waist and what traditionally were called child-bearing hips), and I find the standard waist can roll down a bit. I don't need the zip pocket, but I really like the height of the high waist.
I'd say I'm currently a size 12 in most high street stores for my bottom half, and I'm happier in a size S from Tikiboo (as a guide). They're tight to get on, but they should be! I find the size Medium is fine, and I'm wearing them, but I can feel them slightly slipping down.
My third pair then, was a size Small and High Waisted, and I ordered them in capri length, rather than the long, as the weather is getting warmer (yey). They're fab and I'll be ordering more!
My only criticism is that the designs often seem a little too childish for me, but they assure me some collaborations with illustrators are coming (unlike their recent collaborations with Hello Kitty, Mr. Men and Candy Crush). They've sold well, but really not for me.
I also bought a Boobuddy from Tikiboo - my review is here.