Going back to fountain pens a few years ago helped me. Getting into flex nibs helped me even more.
Mind you, it's not that changing your writing instrument will magically improve your hand writing. It doesn't.
All it does is free you from bad writing habits acquired with the writing instruments you are used to. This allows you to start fresh and get it right this time... with practice, of course, and good work sheets/workbooks, etc.
It's also that a more challenging writing instrument does just that: challenge you. You always get better results when there's a challenge involved.
It's like changing your work-out routine, learning a new language, or learning to paint or pick up a musical instrument. You know, brain flexing.