If you have the Dreamscarred Press psionics books for pathfinder, take a look at a Psion with the Egoist specialty, and the Metamorph prestige class at lvl6. Take every power in the Metamorphosis line as early as possible, and spend nearly all the rest of your powers known on other combat buffs. For feats, start with Overchannel, then take anything that boosts your natural attacks. You're not proficient in armor, but you don't have armor-derived spell failure either, so start with MW leather, and upgrade when you can to mithril chain shirt, but don't wear anything with a check penalty, you can't afford the loss of attack bonus.
I'm running such a character now, and he makes for an unarmed brawler with very much the same mechanical feel as a monk, but much stronger to carry your own weight and appease the optimizers in the group. Mine is fluffed to emphasize the mystical aspects, but fluffing in the other direction should be easy enough. You'll not want the scouting secondary focus my guy has, since that depends heavily on using metamorph to become very small, and will probably want to avoid any of metamorph's size-change options, which can be good in certain fights, but the main metamorph options you want are the natural attacks (go for slam, a body slam doesn't tie up your arms if you decide to carry a mithril buckler or keep a ranged weapon at the ready) and fast healing. Both of those, and most of the other metamorph options that you'll want to use often, are easy to justify non-mystically (the Barbarian can get variations of most of them), and the shape-changing effect's blatant mysticality can be easily averted by always choosing your own natural appearance for the shift.