Just to say, the tunic and leggings look absolutely screams out "I've got no body confidence". It isn't a flattering look on anyone - it is just an easy way to dress. I' sure you deserve a lot better.
You are actually average size in the UK now. I'm a size 20 - I've been taking medication that piles on the pounds for 30 years - and while I won't claim to like looking at my naked body in the mirror, full of stretch marks and God knows what, I'm perfectly happy and confident when dressed. My favourite shops are M&S (particularly Autograph), H&M, Mango, Monsoon (super generous on the sizing!), Joanie (some) and even Primark. Then I really like some dresses etc. from F&F and TU, but always go a size up. Never be afraid to go a size up if it looks right. There is nothing more guaranteed to feel uncomfortable than something you like, but that is pulling in the wrong places. My father's wife will only buy her size and I find that ludicrous. It isn't like you look at the size on the label every time you pull something on!
Don't torture yourself by going into shops that won't have much. I'd be incredibly hard pushed to find something in Next because their body shape just isn't mine. I may well be missing out, but it is too much of a mission. I also choose my trousers very carefully from M&S, as some fit perfectly and others cut my circulation off. But only the size 8s among us can wear anything - everyone from 10 up has a shape and has to choose.
For people who can lose weight, I've read something somewhere that actually just feeling better in your clothes can be the catalyst to losing weight. That sounds entirely counter-intuitive, but it is because the self-loathing lifts and you start to get in contact with your potential.
If you have even the slightest suspicion that your bras don't fit (back rides up, straps fall down, middle doesn't sit tight on your skin, you can feel them under your arms), then I'd suggest you start there. It is amazing how much more you can wear when your underwear is doing the right job. You don't have to spend a fortune. Yes, expensive bras are nice, but then you have to wear them until they die, just to get a return on the investment.
You can so easily look nice as a size 16. You have so many things to choose from. But ditch the leggings and the tunics because you don't need to signal to the world that you're not happy in your skin. Look like you are and you soon will be.