I think Linda Porter's The Myth of "Bloody Mary": A Biography of Queen Mary I of England would be a good one for you. It's written in a very readable style, so I think it counts as "entry level"! At the same time, when I read it I noticed Porter slipping in source criticism and historiography, which you unfortunately often don't get in pop history.

Mary is a great window into the period because an author will need to explain the political situation of her parents' marriage and divorce, as well as Henry VIII's subsequent marriages and how they ended, in order to give the context of Mary's situation - but will generally not go into intense detail, since that's not the topic of the book. Having Mary as a focus (rather than just Henry, or just one of his marriages) also allows the author to cover the later reigns of Edward and Mary herself, which are technically also part of the Tudor period.