There's some great advice on this thread. I agree with the posters who suggest shopping your own wardrobe as a first step. Take a look at what you've got, see if there are different ways of putting things together and layering them. Experimenting can be fun. I'd try your blue dress with a bright-coloured belt or ribbon around the waist, or maybe with a huge brooch on the shoulder, with a cropped cardigan or jumper, with knee-high boots, or peeking out from a trenchcoat. Using Dylon on neglected items can give them a new lease of life and is great for experimenting with colour.
Then add in two or three new pieces that will make new outfits with each other and with what you've got already - stripey top and Chelsea boots have been sensible suggestions here. I'm another one who agrees a soft blazer or jacket can really make a casual outfit shine. Jersey, tweed, a tuxedo, a shacket - they all give a totally different put--together look that's wearable and confident. Other items that can change or upgrade a look for me are: a white shirt, a necklace, a belt, boots, a hat. We're coming to the season when your clothes will mostly been seen glimpsed under a coat - so knitwear in strong colours, which will look good with a winter scarf over the top, is a useful buy. Personally I'd stay away from patterned jersey dresses unless you love them, as they're rarely flattering. Patterns in general make it harder to look good, and if you're on a budget you'll want to repeat wear clothes often - patterns are less versatile and make it more obvious you're wearing the same thing again and again. Plain colours look more harmonious, and can be combined in more ways. BUT enjoyment of what you're wearing should be the top criteria so feel free to ignore this advice! Remember just because others find something a staple doesn't mean you have to wear their uniform. I never wear jeans, for example. We live in a time when there are a lot of things out there to try and you can have fun experimenting to find what's right for you. Clothes are fun.
Get used to your new outfits for a while, start to try on more stuff and you'll begin to work out what you like and what works for you. Don't buy anything unless it makes you smile when you look in the mirror.
I like the Uniqlo merino jumper, though I think the pale blue looks a bit wishy-washy. I have a couple of colours of the crew-neck version. Great as an extra layer, looks good under a jacket, over a shirt, with skirt or trousers, even dressed up with a long multi-strand necklace (not sure this would work with a v-neck though), and maybe with a scarf. My favourite jumpers come from Uniqlo and Cos. You can often find nice M&S cashmere on e-bay at good prices.
I find an easy pick-me-up is lipstick. A bright or dark colour immediately makes your appearance and outfit look bolder and smarter - people look at you and assume your whole outfit is a confident statement rather than a few things you've chucked on in a hurry.