I'm writing a lecture notes with lots of formula in notebook which will be saved as pdf later. In my notes many DisplayFormulaNumbered cells were used, where the default FontStyle were Arial, which looks like(I have converted it to traditionalform):

However, I prefer the formula style displayed in input form which looks like(have been converted into traditionalform):

After looking into the Font of cells by toolbar I found that the default FontStyle of TraditonalForm of InputForm was Times New Roman. Then I try to set the font of DisplayFormulaNumbered cells into the same style, however, this font option is missing in toolbar:

Err...How could I combine the advantage of automatic formula Numbered DisplayFormulaNumbered cells and good-looking formula style?
By the way, suppose I have(I do have!!!) a notebook with many ugly-styled DisplayFormulaNumbered cells, how could I automatically change these cells to desired style?