"Wear cotton" is common advice for eczema, and plenty of people do find scratchy wool or synthetic fabrics make their skin worse. But it's not universal, some people don't notice a difference at all. Rather than replacing a whole wardrobe on a guess, it's worth actually tracking what you wore against how your skin felt.
It's easy to blame "the wool jumper," when actually it might be the detergent it was washed in, or that it was a hot day and any fabric would have felt irritating. Noting fabric, detergent, and how hot or sweaty you were, all in one place, makes it much easier to tell which one is actually doing something.
One itchy evening in a new jumper isn't proof of anything on its own. Comparing several wears against several days in different fabric, over a few weeks, is what turns a hunch into something you can actually trust.
This is general, practical information, not a diagnosis or treatment recommendation. If a specific fabric or product seems to cause a strong reaction, it's worth mentioning to a doctor or dermatologist.
This is exactly what I built SkinFam for, a private, on-device diary where a quick daily note on what you wore sits right next to how your skin felt, so patterns are easier to spot over time. Nothing you log ever leaves your phone. Get SkinFam free on the App Store.