I'm no oil painting but even I have to agree that I look MUCH better with make-up. I am 5ft 4in, 16-18 too. I'm with you on the clothes / style thing though, there are larger ladies who are in proportion, but I am not one of them and I carry so much weight around my middle and look pregnant.
Putting make-up on will add an extra 5 minutes to your morning routine but will make you feel heaps better. This is what I do
Foundation - (maybe a tinted moisturiser would be best for you with dry skin) - I use a liquid applied with a sponge.
Eyeshadow - find a pale peach and just apply with a brush, as it's such a pale colour you can go right up to the lids and it does make your eyes look bigger - this colour suits everyone's eye colour.
Mascara
Kohl pencil on eyeline, or I have a very thin brush and will dab black eyeshadow on it which doesn't create such a harsh line.
JML Magic concealer (this is a powder but it works miracles on me and makes my skin tone look more even).
Just a sweep of blush (or bronzing pearls in the summer)
I only wear lipstick on a night out. I don't wear gloss at all as I hate how it feels. For everyday I just use a tinted lip-syl type of thing
My office is semi-casual (not smart, but definitely no denim). I like jersey dresses worn over leggings which I usually wear with heeled ankle boots, or slouchy suede flat boots. The Jersey material skims rather than clings which is a confidence booster.
I bought some nice jeans this week - cigarette leg from Next at £26. They are a more relaxed fit and more flattering than skinnies.
I went on a Gok Wan show once (not the one where you take your clothes off). I was only in the audience but he told you your body shape and how best to dress it, and apple shapes should wear a jersey blazer which is nipped in at the waist and creates the illusion of actually owning a waist.
I went through a phase of bras being really uncomfortable so I bought some non-wire ones which were okay but i had to admit the wired ones made for a better support. Why not open an account with Very so you can try them on in different sizes in the comfort of your own home - take some before and after photos to see if you can see a difference - if you don't like any of them, just send them back. I am afraid once you get to a certain age or size you definitely need the support. I've just bought some new bras and can see how the other ones had become baggy and a bit shapeless, and how much of a difference they make to my boobs.
Sorry to go on.