Crank Arm Advice Needed

Hi All,

I have a 2017 Cube AIM SL, came with Acera crank arm on a this crankset. (Shimano FC-M3000, 40x30x22T, 175mm) It has become slightly rounded and therefore now becomes loose on most steep hills just when you don't want it to! Have tried the locktite etc tricks.

Should I just replace arm, like for like (although seems difficult to find just the left arm), or should I upgrade slightly, I don't have a huge budget to throw at it and I don't want to end up changing a load of other components for same reason but if I can get a newer version for similar cost, is it worthwhile upgrading? Current Cube Aim has Shimano FC-MT101, 40x30x22T, 175mm and if so, where would you recommend ordering from? Is there a third option I've not thought about?

Thanks so much in advance!