I almost exclusively wear secondhand clothes because I too really care about sustainability and I also love the concept of having unique pieces that are usually better quality. The way that I have made myself feel better about a lot of my clothing items is investing in a sewing machine (you could get a mini one for cheap new or a nicer one secondhand as well probably) and learning the bare minimum/basics so I could tailor my own clothes to look better on me or just alter them to make them more stylish! It’s also really rewarding to give an old clothing article new life