I always recommend just a fresh install on a new SSD.
Given a large, full HDD, going to a much smaller SSD....you don't have a lot of options.
For a migration, it MUST be smaller than 80% of the space of the SSD. For instance...a 256GB SSD - less than 200GB
For a 128GB SSD, less than 100GB.
There is one application that can probably move only the OS, but it is not free.
http://www.paragon-software.com/technologies/components/migrate-OS-to-SSD/
And you may end up with issues later.
Reinstall clean on the new SSD.