Just wanted to say congratulations, OP - you sound like you completely deserve to spoil yourself.
Have you thought about making a Pinterest board? Just put things you like on it, and eventually you should start seeing your style emerging.
I can't recommend Levis highly enough for jeans. The staff are really helpful and the jeans are so comfy. Also, GAP.
Boden are great for basics - t-shirts and cotton shirts are really long-lasting. I'd only go for plain stuff though, as the patterns are a bit lairy and you might get bored.
Clarks do the most comfortable brogues in the world. Hamble Oaks are great and this season I've got some burgundy Somersets. They look great with rolled up jeans, and dresses or skirts with tights.
Hush do an amazing plain black blazer that goes with everything. Their ruched skirts are fab too, and are flattering on a tummy (I know the feeling).
Whistles do brilliant wool coats for not too bad prices.
If I were you, I'd go spendy on a set of basics - a good coat, bag, pair of boots and pair of leather shoes, a really good white shirt and a decent jumper (cashmere). Also a classic dress in black or navy. Get things that will last forever, that will form the backbone of your wardrobe.
Then have some fun with the rest - get some fashion stuff in colours that you like, scarves, funky t-shirts, colourful Converse, etc. Funk your classic pieces up a bit, iykwim.
And buy yourself a really lovely signature scent. Every time you spray it on you can remember this time in your life when you started building the new, glamorous you!