Sources

1) Source: Cosmas of Prague, The Chronicle of the Czechs "He [Ulrich] had no child of a legitimate marriage because of the infertility of his spouse, but of some woman called Božena of Krezina, he begat a son of striking beauty and named him Břetislav" (Data from secondary evidence)
2) Source: Cosmas of Prague, The Chronicle of the Czechs "In the year of the Lord’s incarnation 1052. Božena, the wife of Duke Ulrich and mother of Břetislav, died" (Data from secondary evidence)
3) Source: Cosmas of Prague, The Chronicle of the Czechs "In the same year, on November 9, Duke Ulrich left the earthly realms and reached the celestial." (Data from secondary evidence)
4) Source: Cosmas of Prague, The Chronicle of the Czechs "His wife Judith, of most noble origin and fertile in offspring,gave birth to five boys...The first born son was named Spytihněv, the second-born Vratislav, the third inline Conrad, the fourth in descent Jaromír, the fifth and last was Otto," (Data from secondary evidence)
5) Source: Cosmas of Prague, The Chronicle of the Czechs Bretislav's death in 1055 is described in detail by Cosmas. (Data from secondary evidence)