Solutions to migrate databases
Assuming your are able to code I'd write a conversion tool which reads from one database and writes into the other. That way you'll be able to do any conversion you like, do additional checks on the data and you could even have the program test the result. Just pick your favorite language. Any tool will still require you to define all the conversions one way or another, you'll still have to test etc. So the overall gain of a special to won't bee that big, and you'll have to learn it first. Assuming it's a one-off it probably simply isn't worth the effort to find a learn a new tool.

If you are planning to do these kind of conversions more often that might change though.