If you want real fine grain in 35mm you can develop with an Ultra Fine Grain type developer.

Actual still in commercial availability:
Perceptol
CG-512/RLS
W665

But they have all the disadvantage that you will loose at least one F stop and the sharpness will be less. In theory the Ultra Fine Grain developers based on Phenylene Diamine will have the smallest grain. W665 (Windisch) is based on Ortho Phenylene Diamine.
This developer works very well on e.g. Fomapan T200 film (E.I. 80-100).