Be happy, you’re leaving the old days for a better time. That’s priceless. Don’t use sad notes, i mean, you’re leaving for the better things right?
Write a happy letter, celebrate, encourage your employee friends that you’re taking a different path and that their choice to stay in the company is right, cheers your ex-bosses, don’t tell them how suck they are because they already know, express that you are embracing a better brighter future and cheer yourself up.
May you have all the best luck in your future workplace.