Not sure if any of these have been suggested, but if they have treat it as another vote for them!
https://us.shein.com/Cut-Out-Heart-P...real_1862~~~~0
https://us.shein.com/4pack-Floral-Em...real_1862~~~~0
https://us.shein.com/Cut-Out-Fishnet...real_1862~~~~0
https://midnightrouge.com/collection...ng-panties-set
I do love your coin flip idea - if you wanted to make it riskier, lay out the 4 pieces of clothing before flipping, so you don't get to choose a 'safe' bra the days you lose your top! You can also think of noe task you have to do/place you have to go in the day, to keep you from hiding completely away.
Be careful involving school though - make sure you can always appear presentable enough there, as it is not worth ruining that for a quick thrill.