I would be satisfied alone with the go kart-like abilities and nimbleness of the 135i but if you're really hankering for that addictive diesel torque and acceptable fuel economy, definitely jump on a CPO.
Think it's going to be a bit tough finding a new one now that has your color and options but there should be plenty of CPO 335d vehicles around.
I haven't hit 60K yet but with almost 23K (bought new) under my belt, the only problems I've had were the common "service engine soon" and "brake/traction" warning lights which the former was resolved with a software update but the latter is still an issue. Then I get the usual squeaks in the suspension and an occasional clunk when reversing at certain angles.
So I can't say you have nothing to worry about but hopefully the 100K warranty on a CPO would ease your mind. Good luck!