For starters, in order to utilize Martial Arts, you must take the Martial Arts I-IV quality at a cost of 5 BP x quality level and specify an art. Each level allows one of the advantages supplied by the art and two maneuvers. (Note: the maximum number of dice added or subtracted from combat rolls from these advantages is limited to the level of the relevant combat skill, unarmed for you, and I believe that a +3 DV is listed in the errata.)
To clarify, the martial arts you are referring to is probably Muay Thai (Kickboxing or Savate). You may choose from these advantages: +1 DV on Unarmed Combat attacks (may be taken twice for a cumulative +2 DV); +1 on Defense Tests against unarmed attacks; +1 Full Parry. So, if you took Martial Arts IV (Muay Thai) at a cost of 20 BP, you would get all of these benefits and a choice of eight maneuvers. Other combat styles associated with pit fighting include Wrestling (Glima, Sumo, Brazilian Jiu-Jitsu), Boxing (Musti Yudha, Rince an Bhata Uisce Bheatha), or Sangre y Acero (Eztlitzli, Ars Cybernetica), a pit fighting style specialized for augmented fighters.
With a low Body value, you will probably want to take maneuvers like Disorient, Evasion, Ground Fighting (you'll probably be knocked down a lot), Riposte (you'll have a lot of parry benefits), or Watchful Guard.