Can't select 7.4 mm font size for some fonts, no precise font sizing allowed?

[Tobbinloggin]

Only select fonts have specific font sizes, and this is a problem for me, I tested extensively and found that with a Font Size of 7.4 and a Line Spacing of 6.6 "units" (what is a unit in mms btw?) the words line up on lined paper perfectly, I wanted to write using a different font and sadly found that I cannot select the 7.4 mm font size with other fonts, meaning I'll need to figure out the perfect line spacing for EVERY font that I want to use with lined paper, if you know of a way to convert my line spacing to work with other font sizes, or for the other fonts to have a 7.4 mm option I'd be ever thankful.

Thanks in advance!