I've always wanted to roleplay as a githyanki infiltrator, the creche path to the cure and the whole githyanki thing intrigues me the most in the story. I also want to choose a martial class that I've never yet tried, which is monk.
Don't need to make it the same character though.
A gith melee wizard plays similarly to a monk, and has a better AC. Try illusionist or enchanter to be good at infiltration. Or Rogue - a martial class who isn't actively impeded by armour and can attack with STR so long as they use a finesse weapon. Assassin is good at infiltration, and so is an arcane trickster with the right spells.
But if you must play a gith monk YOU NEED DEX and as much CON as possible too.