Well the most obvious one would be Henry VIII's decision to cast aside Catherine of Aragon and marry Anne Boleyn and break with the Church of Rome in the process. There was Henry VIII's decision to have Anne Boleyn tried for adultery and treason and executed. Going back further, there was Henry VII's decision to launch an invasion of England from his exile in France and battle with Ruchard III to wrest the crown from him. There was Edward VI's decision to come up with his own device for the inheritance of the crown, in effect trying to nullify his father's Act of Succession leaving the crown to first Mary and then Elizabeth if Mary failed to produce heirs. Edward wanted to leave his crown to Lady Jane Grey and her heirs, if any.Following on this path, there is Lady Jane's decision to go ahead with being named queen in lieu of Mary Tudor, even though the majority of the country believed Mary the rightful sovereign. Then there was Mary's painful decision to execute Jane after the failure of Wyatt's rebellion.There was Queen Mary's decision to go ahead with marrying Philip II of Spain, even though this was not a popular move as far as the people were concerned, since it effectively made a Hapsburg the King of England, even though he was not granted the Crown Matrimonial. These are just what I can think of off the top of my head. You could literally write a book--as many have already been written--about these subjects, but this means there is at least plenty of source material for you to work with.
And of course the 'significant decision' to execute Mary Queen of Scots which contributed to the launching of the Spanish Armada to invade England.This decision might be interesting to write about because Elizabeth then denied ever making the decision. There are letters from her to James, Mary's son, essentially saying - 'ooops! I'm so sorry, I had nothing to do with this.'Plenty of material available with this one as well
All comments are moderated so your replies may not show up immediately. Please be patient. Thanks!