In all honesty, it makes very little difference if a woman is "fatter" than you.
If she takes care of herself and wears things that suit her shape she will of course look good.
Beauty isn't defined my size.
I'm far fatter than you, I feel confident in my style choices and always so how lovely I look.
May I suggest a few things?
Skincare, it's very important to start with a clean and clear base.
It doesn't have to be overboard, but cleansing and moisturising your face twice a day can be a game changer.
Make sure your brows are "natural kept". For example, reasonable thickness, filled in with a suitable shade. (Always go a shade lighter if in doubt)
Colour correction is another game changer in getting smooth, blemish free and even skin tone. You can pick up primers or pallets that do this.
For your hair, go straight for a colorphlex on amazon. (Same as olaplex but you can do it at home) it costs less than 7 pounds and trust me, your hair will be swishy and glossy.
If you are having one of those days where you cannot be bothered to "dress up" and are in vest and skinny jeans/leggings/jeggings then dress it up with good boots and a nice classic jacket. Throw on some accessories.
When going out, curly hair is always a nice style and can make you look better than straightened hair bunged up.
If you can't be bothered to curl it grab heated rollers or sleep in rollers.
As others have said, good bras are key. Curvy kate has a nice range.
They can change your body shape if correctly fitted.
To be honest op, size 14 is just a number. You have a few curves and they can be a good thing.
Makes some pinterest boards and get shopping.