Although, it seems like this is as simple as just buying slow fashion apparel, it's not. The root intention of buying sustainable clothing has to do with investing in long lasting pieces, which means buying more mindfully, and basically buying less as well (leading to less consumption). So, we suggest you slowly start investing in labels like Doodlage, Little Things or Korra. All of these can cost you under or around 5K.
PS: If you have old clothes lying around the house you can donate them to Goonj, an organisation that works on upcycling old clothing to make sanitary napkins for women.