Look for a docile species all you want, there is absolutely no guarantee that the snake you choose won't become aggressive or tag you. Find something you like and then find out if anybody has any docile animals they want to sell.
I honestly wouldnt worry about get tagged by something like an american garter if you already have a boa constrictor, they can give a nice solid bite.
The world is your oyster (provided you have the cash). Maybe look into texas leucistic rat snakes, taiwanese rat snakes, mexican black kings, honduran milk snakes, peublan milk snakes, cali kings, brown house snakes(highly underestimated as a great pet snake), yellow rat snakes, carpet pythons, amazon tree boas, spotted pythons.
Bites from most small non venomous aren't very painful and the thought of getting bitten is often more frightening than the bite itself.
Anyways, good luck