My wife died in 2018 should I file as married, single or widower?

Very sorry for your loss.  In the year that your spouse passed you could file a joint return.  Since that was in 2018, now for 2019 you will file as Single unless you still have dependent children that you are supporting.  If you still have dependent children you file as Widower.

If you will file Single, it would be best to start your own new TT account with a new user ID.  If you try to use the old account that had been used for joint returns, it can give you errors as you work on the return and try to file, since it is quite difficult to remove all of the spouse information that is there.