It's tricky isn't it. I get the white shirt problem. Maybe try it buttoned up under a tank top, for a dark academia look? Love a tank top, you can wear them over pretty much anything and they create a neat silhouette, esp with widelegs.
As for tops - recently I got one from Oliver Bonas, with exaggerated puff sleeves that should be all wrong for my shape (tall, quite busty, broad shouldered), yet it looks fabulous IMO! Looking forward to wearing it with widelegs when it's warmer.
I also have a fair few tops from Boden. They've always been more robust than most high street clothes, hope they hang on to that. I tend to go for woven tops with some interest around sleeve or neckline, in white (hah! it's always bloody ivory) and navy.
Other haunts are M&S (their cords are perfect for winter), Uniqlo (though not so much these days), and Seasalt for countryish things (that can also be styled to look more edgy). Mixed in with ME+EM and other expensive brands on sale. And I've had great things from H&M, Zara and New Look.
I vaguely aim to mix posh with casual. So a smartish jacket with a tshirt and jeans. A hoodie with tailored trousers. A combat jacket with a tea dress. But nothing too exaggerated - the hoodie will be trying to look expensive rather than street, and the combat jacket will be well made😁Yes I'm a midlife cliche! But it's popular because it works, it's comfortable, and doesn't make you feel over- or under-dressed. Hope this helps!