It is best to have an career in designing after 12th arts.
I think i may not say that whether it will be best for you or not as it totally depends upon your interest and passion for that particular field.
But i can say it is relevant to go for B.Des course after arts. There are multiple scopes in Arts fiels such as:
Graphic Designer.
Design Managers.
Textile Designer.
Teachers.
Outside Sale Representative.
Costume Designer.
Fashion Stylists.
Fashion Forecasters
You can even go for Masters after qriting UCEED exam.
All the best!!