You can definitely look fashionable on a budget, and it's great that you have vest tops and leggings etc that you can accessorise or build upon.
I know that Tu at Sainsbury's, George at Asda and Dorothy Perkins stock clothes in your size, and offer some really good value for money pieces, in some really fashionable designs and cuts. You could also try Primark, Peacocks and Matalan websites to check what sizes they stock.
This guide from Dorothy Perkins features some lovely clothes, and provides ideas for how to dress your curves for different settings, such as the office or a night out:
m.dorothyperkins.com/en/dpuk/category/inspire-me-6170514/how-to-dress-your-curves-5966359/home?intcmpid=uk-mobile-hp-row13_pos1_curve
Also have a look at what shape you are - hourglass, apple etc - go online to help you if you need any help, then look at online guides for dressing your shape. They can be very helpful.
There are lots of sales on online and in the stores at the moment if you need some Summer clothes.
If you're after Autumn/Winter clothes, red is going to be 'the' colour. Also, a 40's/50's kind of powdery blue/Air Force blue is also going to be big, as are checks and tweed and quite loose fit 80's style tailoring.
You could buy a few cheap, long sleeve jersey tops in the seasons colours, and some accessories, such as a scarf and bag, but also on trend make up - a red or pink lipstick apparently. Also, you could add to your wardrobe according to what you are comfortable in. I'm not a jeans person, so for me it's pencil skirts, jersey dresses and leggings. You can then easily wear these with different accessories and make up/hair styles relatively inexpensively.
Hello Fashion Monthly magazine is great value at £1, and really gives me great information as to the latest trends and colours. The items they feature are far too expensive for me, but I know what colours and styles to search for in high street shops, EBay and charity shops. If you're comfortable with EBay and charity shops, definitely use these too, they can be great for updating your look inexpensively.