I was thinking every time you change class you lose 1 level, to a minimum level of 1. After a long rest you regain your original level, and 1 ‘charge’ of your next class change (you’re level 8, you changed classes three times before rest, you rest at level 5 wake up at level 8 (whatever class you want to be, sure), but when you change class today your new class is only level 6. Maybe after level 8 you recover 2 charges per rest.

Edit, fixed my after 10 bonus, changed 10 to 8 to be more in line with when other classes get their bonuses