Personally, I'd go with a D&D style. (Old school since '79) GP = 1 xp,
Graduated scale for advancement, say 1200 2nd lvl; 2400 2nd, 3600 3rd, etc (for the fighter, steeper scale for mage and elf) and improving skills/abilities, eg., higher attack dice, body points, more spells, etc. Easy Peasy!