If you like your jeans and practical wear then I'd stick to that but better more expensive versions, and invest in a really decent brand bag (leather), coat, and boots (leather) for every day wear. Tan boots and bag for summer and black for winter (if you wear black, if not then brown/tan fine). If you add one or two nice accessories that go with everything like a simple silver necklace and/or bracelet then that helps to make ordinary outfits look like you've made the effort. I've found (being overweight myself in the past) that fine chains and delicate bracelets can be tricky when you are overweight so go for something a bit more substantial. Maybe a chunkier necklace, something like amber beads or Lola Rose (but nothing plastic). Work out if you like softer stretch fabrics or non-stretch fabrics. If stretchy then make sure they are 100% cotton and of a good weight for the item. Exceptions are if it's (for example) a draped jersey top in which case you'd want the finer weight jersey (stretch) fabric.
Joules is a good suggestion as is White Stuff, Mint Velvet (for dressing up), Seasalt, and Fat Face has some good jumpers etc. If you buy quality then it lasts far longer so it probably works out the same as buying cheap that bobbles and falls to pieces/goes out of shape in the wash. Look at outdoorsy type brands online and see what you like.
Try to work out what colour suit you. There's various colour analysis websites online which you can do a basic colour analysis to work out if you suit brights, pastels, cool or warm tones. If you suit cool brights for example then a jewel green top would look great with jeans. Most people can't go wrong with stripes or a Breton look top on the top half, it always looks good/smart/casual at the same time.
You need enough stuff to have a "uniform" that mixes and matches rather than this top only going with those jeans, etc. Also make sure you have enough of the right socks and underwear to go with your outfits. I buy these from supermarkets as I usually find them good quality, good price and comfortable and I can have lots of them.
And invest in a good fitting bra or 5!