bhai swift dx already comes with Yokohama DB..185/60R15. very good tyres i must say. even better than those offered on dlx variant (turanza AR 10).
from ur location i see live in sindh where roads are not very good and mostly bumpy. i also experienced the same with my dlx.
try to keep tyre pressure @ 30 psi in all 4 tyres...it will surely help. it has made a lot of diff for me atleast