Not much out there for 35mm format unfortunately. But why reject filters and other modifications in front or in back of the lens? That’s what Hollywood cinematographers have done for years. A grease smear on a clear filter, stockings on the front or back of the lens, stretching Saran Wrap over the lens etc etc. not to mention all the soft focus filters by Zeiss, Kodak, etc. Even in larger formats the soft focus lenses are somewhat on the long side, like the 85mm Pentax lens