What did you get when you searched the Internet for "migrate sql server postgres"? I got so many hits I can't count them all. Google or Bing can answer that question in a few minutes, where as posting it here could take weeks to get an answer that might not be as complete.
Depending on the importance of your database you should consider hiring someone who specializes in this type of migration. Why? Because it can be very time consuming to migrate between systems with different data types and structures, and the end result needs to be optimized and maintainable. Banks, on-line stores, and other companies whose existence depends on their PostgreSQL database would rather hire a migration specialist with lots of experience to do the job quickly and efficiently rather than tie up their internal resources for several months and hope they do a good job. For example: does your company have a pl/pgsql expert that will rewrite your tsql so it is optimized for PostgreSQL? (Disclaimer: I am not a migration specialist and make no recommendations on who to hire.) Just a thought for your consideration.