Part of me wants to say ARCH SUPPORT, but that's not my hardest item to find even though it is difficult.
No, my real trouble is non-knit long sleeve anything. And just writing about it? without an epic bleepfest of the most original spanish&English jumble of profanity any of you will ever come across (with a small bit of Finnish ugly words thrown in for flavor)? Is hard, y'all. Because I have so much love & respect for members here, it's taking a lot of braining to make the words go (without resorting to curse words in multiple languages).
If it is woven and goes on my top half, it's just a miserable experience trying on woven long sleeve items. Shirts, jackets, coats, whatever. If it isn't my chest, it's my arms. Anything with buttons probably gaps across my chest unless I size up to plus sizes, and I had this problem long before I gained this weight because of muscles in my shoulders and back. IF it fits across the chest without pulling/gapping, it is going to be ridiculously huge around my abdomen or heinously tight on my upper arms (or both). I have literally tried 3 sizes larger and STILL felt sleeves cutting off circulation to my hands. Sleeve length is a problem, too. Most non-tall long sleeves just feel too short (be they knit or woven), and I'm not even tall for heaven's sake! This means I LOOOOOOOVE me some extended sleeves.
I gave up on shopping for woven garments for my upper half about a decade ago because it's just too frustrating. If I can find something that works, it's going to need some many alterations that it's stupid. If the alterations are possible (which is questionable because then you're completely remaking the garment), they're so expensive that I'm not even going there.
So I'd say woven long-sleeved jackets, shirts, coats, blouses, and etcetera that actually fit are so hard to find that I will not be shopping for any of them unless it is the last available option. I had to buy a new winter coat a couple of years ago, and that was a soul-sucking experience that I am not eager to repeat. I am praying to the shopping gods & goddesses that thestate coats I bought still fit in spite of the weight gain because I do NOT want to have to take money from the house budget just to go and be demoralized by the experience of shopping for a new winter coat.