It sounds like we are similar shapes. This summer I have lived in:
Denim shorts (boy fit) from Sainsbury's- run up okay sized, 12 fits well
Denim shorts and linen looking shorts from Matalan- went for a 14 for a looser, comfier fit. These are £10-12 a pair, and are a nice length, a bit longer than mid thigh/above the knee, so cover the worst of the wobble.
Tops- again Matalan for basic plain vests, h&m has some fun prints but you need to try on. I like quirky t-shirts for day times, and my go to places are bershka, Zara and pull and bear (online), they do really cool ones for £6 each.
For evenings, I find that jumpsuits are my go to. In particular, ones with a wrap front (easier to go for a wee in!) and cullotte bottoms. Asda have some nice cullottes in for evenings too, althougj the sizes aren't great, but I have 3 pairs of the Zara ones in different prints, £20 a pair but I live in them.
I struggle for tops for an evening, so I'll check back on others responses for myself!