What if I used Turbo Tax, but not online?

If you used the Desktop Turbo Tax program you should transfer from the Amended 2018 return.  

What if I already transferred my 2018 original data  to do my 2019 taxes before I amended 2018

If you transferred your 2018 data to your 2019 tax program before you prepared your 2018 amended return you did not transfer the amended data.  You will have to delete the 2018 data imported into your 2019 program and then import your 2018 data into your 2019 program to have your amended return data imported.

What if I already filed my 2019 return and have not yet amended my 2018 return, but plan to? I do not think that the change to itemized deductions that I am making in the amendment will affect my 2019 taxes, but should only affect the history and comparison information on forms generated "For your records" in 2019 and going forward. Is it possible to have that updated for my records going forward?

The only way to have the updated info transfer going forward, would be to amend the 2018 return, and then re-do the 2019 return after transferring the amended data from 2018.

However, if the 2019 return is correct, you probably don't need the amended information from 2018, so I suggest you leave the 2019 return alone.