The x300 STX board takes 12V as input too, these are generally easier to source. If the 4x2" form factor suits you, they come in very low profile versions:
https://www.digikey.nl/en/products/detail/eos-power/ULP180-1012/10124857
https://www.digikey.nl/en/products/detail/cui-inc/VOF-180-12/7695855