Need Suggestions: Schema/Menu for font-manipulation

Hi! I am trying to build a WYSIWYG rich text editor with some additional custom plugins but am stuck on what to do when it comes to font manipulation. I am right now using the prosemirror-menu APIS for my menu but I couldn’t find any method for building a menu item for a non-toggleable mark like a fontSize. Would really appreciate any suggestions you guys can give on how to do this. Will it be a better idea to build my own menu component or is there a wayaround.

Thanks in advance