If you want to optimize for legibility rather than speed, a fountain pen with a stub nib might help. Stub nibs are designed to make handwriting look a bit like classic cursive with no effort from the person. But they can also improve handwriting legibility by providing a particular feedback, basically, it stops some bad movements you hand might be doing.

I have most success with nibs which are very smooth but stubby. TWSBI Diamond 580 with 1.1 mm stub nib worked best for me, but it takes bottled ink.