Is the Scarlet Pimpernel too girly/too young?
I must admit I had moved on from them by about the age of 12 to The Three Musketeers and Georgette Heyer (definitely too girly),
However, going back to Sutcliff - don't forget about Flowers of Adonis -- about Alcebiades (Athens rather than Rome). It was my favourite because I studied Greek rather than Roman literature and I didn't discover it until I was 15,
I would recommend Ronald Welch (various periods of history) but they are so prohibitively expensive -- I won't even buy them again myself.
Here is the link to an edited down version of the Jonathan Nield Guilde to the Best Historical Fiction - and at least you can find these for free at Gutenberg.