Handwriting forensics is not my forte but I have contemplated it a bit.
What are your opponent's skills reasonably likely to be in this area? If this is general "looks like theirs" then that is one thing but if they know to look for formations and characters (do you do a with or without the dangly bit at the top, do you put a cross bar on your 7 or 0...), unique quirks (do you start a 6 at the middle point or top?) and combinations of the lot?
Furthermore are they likely to know your language usage style? Even if you got it as unrecognisable as a ransom note then it would all be for nothing if you made the same grammatical mistakes, spelling mistakes, word choices and the like such that it still appeared as you.
Do you have a simpler choice? My handwriting generally looks like a
death metal band logo but if I take time, write in pencil (higher friction, slower results), maybe write all in caps then it looks very different. If I take even longer and use my non dominant hand (I am somewhat ambidextrous, enough to write things at least) then even better still if I am trying not to be recognised as me.
Can you OCR it/transcribe it (or go the other way and take pictures of 50 different pieces of sticky notes/notepaper/whatever and add everything to that) and fire it back through as a handwritten font? Maybe skewing line angles (you probably don't write perfectly straight lines as though you had a parallel), font size, kerning or, or possibly subbing in another character in a few places, or poking it with the "make someone's tits bigger" tool (in gimp that would the warp transform tool these days and available in the main selection of tools, it was formerly known as iwarp), photoshop would be liquify and some combo of those two for whatever image editor you like will probably find that) to make it look a bit less "good"/consistent, possibly also some smudging to simulate that?
You could do most of that with a chain of filters or additional layers you spend a bit of time setting up. Depending upon how much you might want to make say 5 or 6 variations and randomly pick them each time.