I would suggest a bike with a bike more suitible for lower end power, so the bike would be better for all types of riding from trails to tracks. You might be a tiny bit short for a 125 cc, but Kawasakis KX 125s and expecially KTM 125 SX's run pretty small. Or if you dont have the money for a new 125, (because with all the extra fees and things you need your paying over 6 grand) a used bike would be a good decision. Or maybe even look into like what was allready mentioned, a KX/RM 100 or KTM 105 SX :)
Either way, any 2-stroke would be great!