I’m a huge fan of Knix underwear. They’re the most comfortable brands I’ve tried and are incredibly thin, with a seamless underwear design. If you’re interested, you can use my code (wander.lish10) to get 10% off Knix products.
If you’re interested in menstrual cups, I’d recommend Ruby Cup. When you purchase a menstrual cup from Ruby Cup, they also donate one to another menstruator in need.