If you are serious about the rogue/monk, I suggest you take 1 level of Monk, ditch the TWF (since you now have FoB), and take Ascetic Rogue from Complete Adventurer instead.
Get a high Wis score to up your AC. Do NOT take additional levels in Monk (the additional bonusses do not compare with the Rogue class abilities you get).
The Ascetic Rogue will allow you to do Unarmed damage as a Monk of your rogue+your monk lvl.
In addition, there is a difference in the Table short-text and the Feat description. If your DM is lenient enough, he may also allow you to pick up the monk level(s) for Sneak Attack progression.
If that is the case, taking additional Monk levels MIGHT just be worth it.....