Sorry for your loss.  For 2018 you could still file a joint return because that was the year she passed.  If you still have dependent children then you can file as a widower for 2019.  If you have no dependent children, then you will now file Single.

If you file Single, you should start a new account and user ID.  If you were filing jointly on your old account, it is too hard to remove the spouse information cleanly, and it can cause errors for you when you try to e-file.

The filing status available to you for 2019 is Single or Qualifying Widower if you have a qualifying child.  In the year of death (2018) you could have filed jointly. 

You may be eligible to use qualifying widow as your filing status.  See discussion here.

“Qualifying Widow(er)

If your spouse died in 2019, you can use married filing jointly as your filing status for 2019 if you otherwise qualify to use that status. The year of death is the last year for which you can file jointly with your deceased spouse.

You may be eligible to use qualifying widow(er) as your filing status for 2 years following the year your spouse died."

PerIRS publication 501 page 9.

You must have a child you can claim as a dependent.