OP, if this helps, last summer my wardrobe mainly comprised the following items, and I felt pretty fab having lost some weight and bought new clothes (also nearly all on Vinted)
I don't have amazing anything - I slimmed down to a comfortable 16 or a large 14, and I have pudgy arms, thick legs and one heck of a belly, I wore the following clothes and felt genuinely amazing. I made more effort with hair and make up than usual, and donned my sunglasses and hats (and SPF50) and I had the best summer ever.
Couple of long black summer dresses - wide scoop neck or shirt dress style, cinched in at the waist with tan or gold belt and tan or gold shoes, with denim jacket (my dresses were from M&S, Monki and John Lewis)
Jumpsuits (Halara) - stretchy and as comfortable as a baby grow but one item of clothing to think about and look surprisingly stylish
White legged white/ecru trousers (Hush) with belt, vest top and loose linen shirt
White barrel leg trousers (Hush) - wearing all white isn't practical but felt super put together, with tan belt, tan shoes and tan bag.
Cargo trousers, not too baggy (Hush) in different colours but quite silky fabrics- navy, khaki and black - ideal with trainers or flat sandals
Long white linen dress (White Company) - easy to dress up or down
Mix of jeans - dark indigo and paler blue - in flare style but not too wide legged (they make me look wider)
Rotation of vest tops, linen shirts, off-the-shoulder loose t-shirts and more fitted v neck t-shirts (t-shirts with longer sleeves to the elbow) in white, pale pink, pale grey, navy to mix with the various trousers (mostly Hush, Next, Mint Velvet)
Rotation of light-weight jumpers in pale grey, white, cream, pale pink and shawls and ponchos (mainly online)
Gold belt, shoes, bag
Tan belt, shoes, bag
Gold trainers
White trainers
Khaki cap
Straw hat
Sunglasses
Something else to think about - do you have a summer perfume? I feel very different in the summer months than I do the rest of the year, so I tend to wear a different scent and that can make a huge difference!