Sustainable Underwear

Hi! As the title says, I'm trying to find sustainable underwear not made from synthetic fibers. I'm starting to become more and more conscious of just the lack of quality with clothing recently, and I want to make a big switch in my life and closet. For most items, I know to just thrift or buy second hand. But with things like underwear, bras, and swimwear I have no clue where to start or what to do. I just can't imagine ever wanting to use second hand underwear haha. I am a college student who still relies on my parents for most things, so finding new cheap sustainable clothing is a struggle. Are there any good sustainable brands that won't break the bank? I'm okay with splurging because I know quality comes at a cost, but I would still prefer the cheapest choice because times aren't really allowing for dropping hundreds of dollars on 7 pairs of underwear. Would learning to sew and create my own underwear be the best bang for my buck? Is it a difficult process? Sorry for all these questions haha, I'm just starting out. Any and all help is appreciated! Thank you :)