What do you call a 1:3 turn ratio transformer?
Coilcraft are a turn to company and they do a few small ones at 1:3 ratio: -



All you have to do now is ensure that the primary current (25 kHz) doesn't saturate the core. V = L di/dt is the formula to use here. Coilcraft tell you the saturation current so I'll leave it to you to plug the numbers in. Let me know if you need help.

I think these might be too small and will saturate but check out what else coilcraft have to offer and maybe also consider upping the drive frequency to 100 kHz to make life easier on the core saturation.